Wide-Area Networking Configuration Guide: Layer 2 Services, Cisco IOS XE Release 3S (ASR1000)
Layer 2 Tunneling Protocol Version 3
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Layer 2 Tunneling Protocol Version 3

Contents

Layer 2 Tunneling Protocol Version 3

The Layer 2 Tunneling Protocol Version 3 feature expands Cisco’s support of Layer 2 VPNs. Layer 2 Tunneling Protocol Version 3 (L2TPv3) is an IETF l2tpext working group draft that provides several enhancements to L2TP to tunnel any Layer 2 payload over L2TP. Specifically, L2TPv3 defines the L2TP protocol for tunneling Layer 2 payloads over an IP core network by using Layer 2 VPNs.

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the feature information table at the end of this module.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/​go/​cfn. An account on Cisco.com is not required.

Prerequisites for Layer 2 Tunneling Protocol Version 3

  • Before you configure an xconnect attachment circuit for a provider edge (PE) device (see the Configuring the Xconnect Attachment Circuit task), the Cisco Express Forwarding (formerly known as CEF) feature must be enabled. To enable Cisco Express Forwarding on an interface, use the ip cef or ip cef distributed command.
  • You must configure a loopback interface on the router for originating and terminating the L2TPv3 traffic. The loopback interface must have an IP address that is reachable from the remote PE device at the other end of an L2TPv3 control channel.

Restrictions for Layer 2 Tunneling Protocol Version 3

General L2TPv3 Restrictions

  • Cisco Express Forwarding must be enabled for the L2TPv3 feature to function. The xconnect configuration mode is blocked until Cisco Express Forwarding is enabled. On distributed platforms, such as the Cisco 7500 series, if Cisco Express Forwarding is disabled while a session is established, the session is torn down. The session remains down until Cisco Express Forwarding is reenabled. To enable Cisco Express Forwarding, use the ip cef or ip cef distributed command.
  • The IP local interface must be a loopback interface. Configuring any other interface with the ip local interface command results in nonoperational setting.
  • The number of sessions on PPP, High-Level Data Link Control (HDLC), Ethernet, or 802.1q VLAN ports is limited by the number of interface descriptor blocks (IDBs) that the router can support. For PPP, HDLC, Ethernet, and 802.1q VLAN circuit types, an IDB is required for each circuit.
  • When L2TPv3 is used to tunnel Frame Relay D channel data-link connection identifiers (DLCIs), an IDB is not required for each circuit. As a result, the memory requirements are much lower. The scalability targets for the Engineering Field Test (EFT) program are 4000 L2TP session.
  • To convert an interface with Any Transport over MPLS (AToM) xconnect to L2TPv3 xconnect, remove the AToM configuration from the interface and then configure L2TPv3. Some features may not work if L2TPv3 is configured before removing the AToM configuration.
  • Frame Relay support includes only 10-bit DLCI addressing. The L2TPv3 feature does not support Frame Relay extended addressing.
  • The interface keepalive feature is automatically disabled on the interface to which xconnect is applied, except for Frame Relay encapsulation, which is required for Local Management Interface (LMI).
  • Static L2TPv3 sessions do not support Frame Relay LMI interworking.
  • Static L2TPv3 sessions do not interoperate with Universal Tunnel Interface (UTI) using keepalives.
  • Layer 2 fragmentation of IP packets and Intermediate System-to-Intermediate System (IS-IS) fragmentation through a static L2TPv3 session are not supported.
  • Layer 3 fragmentation is not recommended because of performance degradation.
  • The L2TPv3 Layer 2 (IP packet) fragmentation feature (see the Configuring the L2TPv3 Pseudowire task) is not supported when the customer edge (CE) router is running special Layer 2 options such as Layer 2 sequencing, compression, or encryption. Examples of these options are Frame Relay compression and fragmentation or PPP compression. In these scenarios, the IP payload is not in a format that is compatible with IP fragmentation.
  • The Stateful Switchover (SSO), Route Processor Redundancy (RPR) and RPR+ components of the HA functions are supported only at the coexistence level. If you attempt a switchover using SSO, RPR, or RPR+, the tunnels will fail and then eventually recover after an undetermined time duration. This includes both IPv4 and IPv6 traffic.
  • Interworking is not allowed when sequencing is enabled.
  • Untagged packets (native VLAN) forwarding for xconnect that is configured on the dot1q subinterface is not supported.

VLAN-Specific Restrictions

  • A PE device is responsible only for static VLAN membership entries that are configured manually on the device. Dynamic VLAN membership entries, entry aging, and membership discovery are not supported.
  • Implicit tagging for VLAN memberships operating on other layers, such as membership by MAC address, protocol type at Layer 2, or membership by IP subnet at Layer 3, is not supported.
  • Point-to-multipoint and multipoint-to-point configurations are not supported. There is a 1:1 relationship between an attachment circuit and an L2TPv3 session.

IPv6 Protocol Demultiplexing for L2TPv3 Restrictions

  • IPv6 protocol demultiplexing is supported only for Ethernet traffic.
  • IPv6 protocol demultiplexing is supported over noninterworking sessions.

L2TPv3 Control Message Hashing Restrictions

  • L2TPv3 control channel authentication configured using the digest command requires bidirectional configuration on the peer devices. A shared secret must be configured on the communicating nodes.
  • For a compatibility matrix of all the L2TPv3 authentication methods, see the Valid Configuration Scenarios table in the IPv6 Protocol Demultiplexing section.

L2TPv3 Digest Secret Graceful Switchover Restrictions

  • This feature works only with authentication passwords configured using the L2TPv3 Control Message Hashing feature. L2TPv3 control channel authentication passwords configured with the older, Challenge Handshake Authentication Protocol (CHAP)-like authentication system cannot be updated without tearing down L2TPv3 tunnels and sessions.
  • In Cisco IOS Release 12.0(30)S, a maximum of two passwords can be configured simultaneously using the digest secret command.

For more information about the L2TPv3 Control Message Hashing feature, see the L2TPv3 Control Message Hashing section.

Quality of Service Restrictions in L2TPv3 Tunneling

Quality of service (QoS) policies configured with the modular QoS CLI (MQC) are supported in L2TPv3 tunnel sessions with the following restrictions:

Frame Relay Interface (Non-ISE/E5)

  • On the Cisco 7500 series with distributed CEF (dCEF), in a QoS policy applied to a Frame Relay interface configured for L2TPv3, only the MQC commands match fr-dlci in class-map configuration mode and bandwidth in policy-map configuration mode are supported. (See the Configuring QoS for L2TPv3 on the Cisco 7500 Series Example task.)
  • On the Cisco 12000 series, a QoS policy is supported in TSC-based L2TPv3 tunnel sessions on the Frame Relay interfaces of a 2-port channelized OC-3/STM-1 (DS1/E1) or 6-port channelized T3 (T1) line card with the following restrictions:
    • The police command is supported as follows:
      • Only the transmit option for the action keyword is supported with the conform-action command.
      • Only the set-frde-transmit option for the action keyword is supported with the exceed-action command.
      • Only the drop option for the action keyword is supported with the violate-action command.
      • Backward explicit congestion notification (BECN) and forward explicit congestion notification (FECN) configuration are not supported.
      • The type of service (ToS) byte must be configured in IP headers of tunneled Frame Relay packets when you configure the L2TPv3 pseudowire (see the Configuring the L2TPv3 Pseudowire task).
      • All standard restrictions for configuring QoS on Cisco 12000 series line cards apply to configuring QoS for L2TPv3 on Cisco 12000 series 2-port Channelized OC-3/STM-1 (DS1/E1) or 6-port Channelized T3 line cards.
    • On the ingress side of a Cisco 12000 series Frame Relay interface configured for TSC-based L2TPv3 tunneling:
      • Weighted random early detection (WRED) and modified deficit round robin (MDRR) configurations are not supported.
    • On the egress side of a Cisco 12000 series Frame Relay interface configured for TSC-based L2TPv3 tunneling:
      • MDRR is the only queueing strategy supported.
      • WRED is the only packet drop strategy supported.
      • MDRR is supported only in the following modes:
        • With both a low latency (priority) queue and class-default queue configured. (The low latency queue is supported only in combination with the class-default queue, and cannot be configured with normal distributed round robin (DRR) queues.)
        • Without a low latency queue configured. (In this case, only six queues are supported, including the class-default queue.)
      • Egress queueing is determined according to the IP precedence values configured for classes of L2TPv3 Frame Relay traffic using the match ip precedence command, instead of on a per-DLCI basis.

For an example, see Configuring QoS on a Frame Relay Interface in a TSC-Based L2TPv3 Tunnel Session.

Edge Engine (ISE/E5) Interface

On the Cisco 12000 series, a QoS policy is supported in native L2TPv3 tunnel sessions on ISE/E5 interfaces (see Table 2 and Table 3 for a list of supported line cards) with the following restrictions:

  • On a Frame Relay or ATM ISE/E5 interface, traffic policing supports only the following conform, exceed, and violate values for the action argument of the police command:

conform-action actions set-prec-tunnel set-dscp-tunnel transmit

exceed-action actions drop set-clp (ATM only) set-dscp-tunnel set-dscp-tunnel and set-clp (ATM only) set-dscp-tunnel and set-frde (Frame Relay only) set-frde(Frame Relay only)set-prec-tunnel set-prec-tunnel and set-clp (ATM only) set-prec-tunnel and set-frde (Frame Relay only) transmit

violate-action actions drop

  • On a Frame Relay ISE/E5 interface:
    • FECN and BECN configuration are not supported.
    • Marking the Frame Relay discard eligible (DE) bit using a MQC set command is not supported. To set (mark) the DE bit, use the police exceed-action actions command in policy-map configuration mode.
    • Configuring Tofab MDRR or WRED using legacy QoS (not MQC) commands is supported and is based on the tunnel precedence value.
    • Egress queueing on a Packet-over-SONET ISE/E5 interface is class-based when configured using MQC.
    • Egress queueing on a per-DLCI basis is not supported.
  • On an ATM ISE/E5 interface:
    • Traffic shaping is supported on ATM egress interfaces for the following service categories:
  • Lowest priority: UBR (unspecified bit rate) Second priority: VBR-nrt (variable bit rate nonreal-time) Highest priority: VBR-rt (VBR real time) Highest priority: CBR (constant bit rate)
  • Note that VBR-rt and CBR share the same high-priority shaping. ATM traffic shaping restricts traffic to the maximum rate configured on an ATM VC or PVP with due priority among the respective service categories.
  • You can configure queue limits for an ATM VC or PVP. The queue limits are dual thresholds in which two different thresholds can be configured for CLP=1 cells and CLP0+1 cells. The CLP1 threshold must be lower than the queue limit threshold so that CLP=1 cells are dropped earlier than CLP=0 cells when packets start to fill the queue.
    • Although the dual-rate, 3-Color Marker policer is not supported on ATM ISE/E5 interfaces (as on Frame Relay ISE/E5 interfaces), the ATM Forum Traffic Management Version 4.1-compliant Generic Cell Rate Algorithm (GCRA) policer is supported. The GCRA policer uses rate, peak rate, delay tolerance, and ATM maximum burst size, and supports the following actions:

set-dscp-tunnel and set-clp-transmit.

Protocol Demultiplexing Interface

Protocol demultiplexing requires a combination of an IP address and the xconnect command configured on the interface. The interface is then treated as a regular L3. To apply QoS on the Layer 2 IPv6 traffic, you must classify the IPv6 traffic into a separate class before applying any feature(s) to it.

The following match criterion is used to classify Layer 2 IPv6 traffic on a protocol demultiplexing interface:

class-map match-ipv6
     match protocol ipv6

In the absence of a class to handle Layer 2 IPv6 traffic, the service policy is not accepted on a protocol demultiplexing interface.

For detailed information about QoS configuration tasks and command syntax, refer to:

  • Cisco IOS Quality of Service Solutions Configuration Guide
  • Cisco IOS Quality of Service Solutions Command Reference

Frame Relay over L2TPv3

The following are the restrictions for the Frame Relay over L2TPv3 feature:

  • Only Frame Relay DLCI mode over L2TPv3 is supported. Frame Relay port mode is not supported.
  • L2TPv3 PW redundancy for FR DLCI is not supported.

Information About Layer 2 Tunneling Protocol Version 3

L2TPv3 provides a method for delivering L2TP services over an IPv4 (non-UDP) backbone network. It encompasses the signaling protocol as well as the packet encapsulation specification.

L2TPv3 Header Description

The migration from UTI to L2TPv3 also requires the standardization of the UTI header. As a result, the L2TPv3 header has the new format shown in the figure below.

Figure 1. L2TPv3 Header Format

Each L2TPv3 packet contains an L2TPv3 header that includes a unique session ID representing one session and a variable cookie length. The L2TPv3 session ID and the Tunnel Cookie field length are assigned through the CLI. See the section "How to Configure L2TPv3" for more information on the CLI commands for L2TPv3.

Session ID

The L2TPv3 session ID identifies the session context on the decapsulating system. For dynamic sessions, the value of the session ID is selected to optimize the context identification efficiency of the decapsulating system. A decapsulation implementation may, therefore, elect to support a smaller session ID bit field. In this L2TPv3 implementation, an upper value for the L2TPv3 session ID was set at 023. The L2TPv3 session ID value 0 is reserved for use by the protocol. For static sessions, the session ID is manually configured.


Note


The local session ID must be unique on the decapsulating system and is restricted to the least significant ten bits.


Session Cookie

The L2TPv3 header contains a control channel cookie field. The control channel cookie field has a variable length of 0, 4, or 8 bytes according to the cookie length supported by a given platform for packet decapsulation. The control channel cookie length can be configured manually for static sessions or determined dynamically for dynamic sessions.

The variable cookie length does not present a problem when the same platform is at both ends of an L2TPv3 control channel. However, when different platforms interoperate across an L2TPv3 control channel, both platforms need to encapsulate packets with a 4-byte cookie length.

Pseudowire Control Encapsulation

The L2TPv3 pseudowire control encapsulation consists of 32 bits (4 bytes) and contains information used to sequence L2TP packets (see the Sequencing section). For the purposes of sequencing, only the first bit and bits 8 to 31 are relevant. Bit 1 indicates whether the Sequence Number field, bits 8 to 31, contains a valid sequence number and is to be updated.

L2TPv3 Operation

L2TPv3 includes the following features:

  • Xconnect for Layer 2 tunneling through a pseudowire over an IP network
  • Layer 2 VPNs for PE-to-PE device service using xconnect that supports Ethernet and VLAN, including both static and dynamic (using the new L2TPv3 signaling) forwarded sessions

The initial Cisco IOS software supported only the following features:

  • Layer 2 tunneling (as used in an L2TP access concentrator or LAC) to an attachment circuit, not Layer 3 tunneling
  • L2TPv3 data encapsulation directly over IP (IP protocol number 115), not using the UDP
  • Point-to-point sessions, not point-to-multipoint or multipoint-to-point sessions
  • Sessions between the same Layer 2 protocols, such as Ethernet-to-Ethernet and VLAN-to-VLAN, but not VLAN-to-Ethernet

The attachment circuit is the physical interface or subinterface attached to the pseudowire.

The figure below shows how the L2TPv3 feature is used for setting up VPNs using Layer 2 tunneling over an IP network. All traffic between two customer network sites is encapsulated in IP packets carrying L2TP data messages and sent across an IP network. The backbone devices of the IP network treat the traffic as any other IP traffic and need not know anything about the customer networks.

Figure 2. L2TPv3 Operation

In the figure above, the PE devices R1 and R2 provide L2TPv3 services. The R1 and R2 devices communicate with each other using a pseudowire over the IP backbone network through a path comprising interfaces int1 and int2, the IP network, and interfaces int3 and int4.

In this example, the customer edge (CE) devices R3 and R4 communicate through a pair of xconnect Ethernet or VLAN interfaces using an L2TPv3 session. The L2TPv3 session tu1 is a pseudowire configured between interface int1 on R1 and interface int4 on R2. Any packet arriving on interface int1 on R1 is encapsulated and sent through the pseudowire control channel (tu1) to R2. R2 decapsulates the packet and sends it on interface int4 to R4. When R4 needs to send a packet to R3, the packet follows the same path in reverse.

Note the following features regarding the L2TPv3 operation:

  • All packets received on interface int1 are forwarded to R4. R3 and R4 cannot detect the intervening network.
  • For Ethernet interfaces, any packet received from LAN1 by R1 on Ethernet interface e1 is encapsulated directly in IP and sent through the pseudowire session tu2 to R2 interface e2, where it is sent on LAN2.
  • A VLAN on an Ethernet interface can be mapped to an L2TPv3 session.

L2TPv3 Features

L2TPv3 provides xconnect support for Ethernet and VLAN using Static and Dynamic sessions.

Static L2TPv3 Sessions

Typically, the L2TP control plane is responsible for negotiating session parameters, such as the session ID or the cookie, to set up the session. However, some IP networks require sessions to be configured so that no signaling is required for session establishment. You can set up static L2TPv3 sessions for a PE device by configuring fixed values for the fields in the L2TP data header. A static L2TPv3 session allows the PE device to tunnel Layer 2 traffic as soon as the attachment circuit to which the session is bound comes up.

Static configuration allows sessions to be established without dynamically negotiating control connection parameters. This means that although sessions are displayed in the show l2tun session command output, no control channel information is displayed in the show l2tun tunnel command output.


Note


In an L2TPv3 static session, you can still run the L2TP control channel to perform peer authentication and dead-peer detection. If the L2TP control channel cannot be established or is torn down because of a hello failure, the static session is also torn down.


If you use a static L2TPv3 session, you cannot perform circuit interworking, such as LMI, because there is no facility to exchange control messages. To perform circuit interworking, you must use a dynamic session.

Dynamic L2TPv3 Sessions

A dynamic L2TP session is established through the exchange of control messages containing attribute-value (AV) pairs. Each AV pair contains information about the nature of the Layer 2 link being forwarded, including the payload type and virtual circuit (VC) ID.

Multiple L2TP sessions, one for each forwarded Layer 2 circuit, can exist between a pair of PE devices and can be maintained by a single control channel. Session IDs and cookies are dynamically generated and exchanged as part of a dynamic session setup. Information such as sequencing configuration is also exchanged. Circuit state changes (UP/DOWN) are conveyed using the set link info (SLI) message.

Control Channel Parameters

The L2TP class configuration procedure creates a template of L2TP control channel parameters that can be inherited by different pseudowire classes. L2TP control channel parameters are used in control channel authentication, keepalive messages, and control channel negotiation. In an L2TPv3 session, the same L2TP class must be specified in the pseudowire configured on the PE device at each end of the control channel. Configuring L2TP control channel parameters is optional. However, the L2TP class must be configured before it is associated with a pseudowire class (see the Configuring the L2TPv3 Pseudowire task).

L2TPv3 Control Channel Authentication Parameters

Two methods of control channel message authentication are available: the L2TPv3 Control Message Hashing feature and CHAP-style L2TP control channel. The L2TPv3 Control Message Hashing feature introduces a more robust authentication method than the older, CHAP-style L2TP control channel method of authentication. You may choose to enable both the methods of authentication to ensure interoperability with peers that support only one of these methods of authentication, but this configuration will yield control of the authentication method used on the peer PE device. Enabling both the methods of authentication should be considered as an interim solution to solve backward compatibility issues during software upgrades.

The principal difference between the two methods of authentication lies in the L2TPv3 Control Message Hashing feature using the entire message in the hash instead of computing the hash over selected contents of a received control message. In addition, instead of including the hash digest in only the start control channel replay (SCCRP) and start control channel connected (SCCCN) messages, it includes it in all messages.

Support for L2TP control channel authentication is maintained for backward compatibility. Either or both authentication methods can be enabled to allow interoperability with peers supporting only one of the authentication methods.

The table below shows a compatibility matrix for the different L2TPv3 authentication methods. PE1 is running the new authentication method. The possible authentication configurations for PE1 are shown in the first column. The other columns represent PE2 running software with different available authentication options. The tables cells in these columns indicate compatible configuration options for PE2. If any PE1/PE2 authentication configuration poses ambiguity about the authentication method used, the winning authentication method is indicated in bold. If both the old and new authentication methods are enabled on PE1 and PE2, both types of authentication occur.

Table 1 Compatibility Matrix for L2TPv3 Authentication Methods

PE1 Authentication Configuration

PE2 Supporting Old Authentication1

PE2 Supporting New Authentication2

PE2 Supporting Old and New Authentication3

None

None

None

New integrity check

None

New integrity check

Old authentication

Old authentication

Old authentication

Old authentication and new authentication

Old authentication and new integrity check

New authentication

New authentication

New authentication

Old authentication and new authentication

New integrity check

None

None

New integrity check

None

New integrity check

Old and new authentication

Old authentication

New authentication

Old authentication

New authentication

Old and new authentication

Old authentication and new integrity check

Old authentication and new integrity check

Old authentication

Old authentication

Old authentication and new authentication

Old authentication and new integrity check

1 Any PE software that supports only the old CHAP-like authentication system.
2 Any PE software that supports only the new message digest authentication and integrity checking authentication system, but does not understand the old CHAP-like authentication system. This type of software may be implemented by other vendors based on the latest L2TPv3 draft.
3 Any PE software that supports both the old CHAP-like authentication and the new message digest authentication and integrity checking authentication system.

Ethernet over L2TPv3

The Ethernet over L2TPv3 feature provides support for Ethernet-based Layer 2 payload tunneling over IP core networks using L2TPv3.

The Ethernet over L2TPv3 feature supports the following like-to-like switching modes:

  • Ethernet port mode
  • Ethernet VLAN mode
  • Ethernet VLAN mode with VLAN rewrite
  • Ethernet QinQ and QinAny mode

Note


The QinQ over L2TPv3 support feature includes QinAny over L2TPv3, which has a fixed outer VLAN tag and a variable inner VLAN tag.


The Ethernet over L2TPv3 feature supports the following types of internetworking:

  • Ethernet port to VLAN (routed)
  • Ethernet port to VLAN (bridged)
  • QinQ to Ethernet VLAN or Port Interworking (routed)
  • QinQ to Ethernet VLAN or Port Interworking (bridged)

Note


QinAny Interworking is not a valid configuration because the inner VLAN tag is undetermined.


GEC over L2TPv3

Gigabit EtherChannel (GEC) over Layer 2 Tunneling Protocol Version 3 (L2TPv3) provides support for GEC-based Layer 2 payload tunneling over IP core networks using L2TPv3. GEC also known as port channel is integrated with Ethernet and dot1q attachment circuits (ACs).

A port channel bundles physical links into a channel group to create a single logical link that provides the aggregate bandwidth of up to eight physical links. If a member port within a port channel fails, the traffic previously carried over the failed link switches to the remaining member ports within the port channel.

Interworking switching is supported in the following scenarios:

  • The customer-edge-provider-edge (CE-PE) connecting interface on the local PE is a port-channel interface without dot1q encapsulation. The CE-PE connecting interface on the remote PE is a port-channel interface with dot1q encapsulation.
  • The CE-PE connecting interface on the local PE is a port-channel interface with or without dot1q encapsulation. The CE-PE connecting interface on the remote PE is an Ethernet interface with or without dot1q encapsulation.

The figure below illustrates a port channel over IP core networks using L2TPv3. CE1 and CE2 are connected to L2TP Control Connection Endpoints (LCCE) and through port channels. The LCCE is connected to the IP core network using L2TPv3.

Figure 3. GEC over L2TPv3

Frame Relay over L2TPv3

The following features are supported:

  • FR DLCI to FR DLCI like2like transparent:
    • Transparent route exists between different DLCIs
    • FR encapsulation type [Cisco or Internet Engineering Task Force (IETF)] can be different on two CEs if they are Cisco equipment.
    • Support end-to-end FRF.12 fragments.
  • FR DLCI to Ethernet bridged interworking
  • On the FR PE side, other FR packets are dropped except the following types:
    • Cisco encapsulation, Ether Type is TYPE_BRIDGE (0x6558)
    • Cisco encapsulation, Ether Type is TYPE_IEEE_SPANNING (0x4242)
    • IETF SNAP encapsulation. SNAP type is Ethernet without LAN FCS (0x0300800080C20007)
  • Local Management Interface (LMI)
  • L2TPv3 sequencing
  • L2TPv3 QoS marking

The following functions are not supported.

  • FR to DOT1Q or QINQ VLAN interworking
  • IP interworking
FR DLCI to FR DLCI Like to Like Mode

In the FR DLCI to FR DLCI Like to Like mode(Figure 4), there is a one-to-one mapping between a Frame Relay Permanent Virtual Circuit (PVC) and an FR Pseudo Wire (PW), supporting bidirectional transport of variable-length frames. The Frame Relay frames are transmitted in their entirety, including the DLCI and the C/R, forward explicit congestion notification (FECN), backward explicit congestion notification (BECN), and DE bits, but excluding the opening and closing flags and the frame check sequence (FCS). The egress PE rewrites the DLCI and regenerates the FCS.

Figure 4. Structure of the FR DLCI to FR DLCI Like to Like mode



FR DLCI to Ethernet-Bridged or Ethernet VLAN-Bridged Interworking

This interworking mode provides interoperability between the FR attachment VC and the Ethernet attachment VC that which are connected to different PE routers respectively. Bridged encapsulation is applied to this mode.

Interworking between the Ethernet port of the PE and the FR attachment VC is based on RFC 2427-(Multiprotocol Interconnect over Frame Relay).

For interworking between the PE and the IP cloud, when the FR segment transmits to IP cloud, the bridged encapsulation FR or SNAP headers are discarded, and the Ethernet frames are encapsulated with the L2TPv3 headers that are required to pass through the pseudo wire via the pseudo wire Ethernet.

In the opposite direction, after the L2TPv3 header decapsulation from the IP cloud, Ethernet frames are encapsulated over FR using bridged encapsulation.

Local Management Interface (LMI)

LMI is a signalling standard that is to manage the connection and maintaining the existing status between devices.

In the DLCI-to-DLCI connection, Frame Relay LMI procedures are applied on the Frame Relay ports that are connected to the PE and CE devices. All LMI types implemented under Cisco IOS are supported, such as Cisco ANSI Q933A.

The PE device will communicate the LMI state between PE1 and PE2 using the L2TPv3 SLI control message defined in RFC3931 to signal Frame Relay link status notifications when the LMI procedure determines that a local PVC has been deleted or is inactive. The SLI message must be sent any time a circuit status change is reported by any of the values identified in the Circuit Status AVP.

Scaling Numbers for Frame Relay over L2TPv3

For Frame Relay over L2TPv3, the maximum session number is restricted by both the maximum number of configurable FR DLCI numbers and the maximum L2TPv3 session supported.

The maximum number of switched FR DLCI VCs per frame relay port is 992(The range is from 16 to 1007), and the maximum number of FR VCs is 7936 per SPA (SPA-8XCHT1/E1).

The maximum number of L2TPv3 sessions is 8192 on RP1 and 16384 on RP2. The maximum number of L2TPv3 tunnels is 2048 on RP1, and 4096 on RP2. One tunnel can carry a maximum of 2000 sessions.

High Availability

On RP switchover:

The L2TPv3 feature in Cisco IOS XE3.12 works in the SSO coexistence mode. This means that all the L2TPv3 sessions will be lost at RP switchover. Pre-switchover sessions are removed from the various control plane modules and then re-established after switchover.

On FP switchover:

Standby FP is already programmed before switchover. Therefore, the standby FP can start handling L2TPv3 traffic immediately. However, it is not possible to checkpoint the L2TPv3 sequence number between an active FP and a standby FP. When the L2TPv3 sequence number is enabled, this number may be out of sync between local and remote routers after FP switchover, while the resync sequence number function should notify the PE to reset the L2TPv3 session and initialize the Ns and Nr to 0. When the number of dropped packets exceed the configured limitation, traffic will be recovered.


Note


The resync function is disabled by default.

Sequencing

Although the correct sequence of received Layer 2 frames is guaranteed by some Layer 2 technologies (by the nature of the link such as a serial line) or by the protocol itself, forwarded Layer 2 frames may be lost, duplicated, or reordered when they traverse a network as IP packets. If the Layer 2 protocol does not provide an explicit sequencing mechanism, you can configure L2TP to sequence its data packets according to the data channel sequencing mechanism described in the L2TPv3 IETF l2tpext working group draft.

A receiver of L2TP data packets mandates sequencing through the Sequencing Required AV pair when the session is being negotiated. A sender (or one that is manually configured to send sequenced packets) that receives this AV pair uses the Layer 2-specific pseudowire control encapsulation defined in L2TPv3.

You can configure L2TP to drop only out-of-order packets; you cannot configure L2TP to deliver the packets out-of-order. No reordering mechanism is available.

Interworking is not allowed when sequencing is enabled.

L2TPv3 Type of Service Marking

When Layer 2 traffic is tunneled across an IP network, information contained in the Type of Service (ToS) bits may be transferred to the L2TP-encapsulated IP packets in one of the following ways:

  • If the tunneled Layer 2 frames themselves encapsulate IP packets, it may be desirable to simply copy the ToS bytes of the inner IP packets to the outer IP packet headers. This action is known as "ToS byte reflection."
  • You can specify the ToS byte value used by all packets sent across the pseudowire. This is known as "Static ToS byte configuration".

For more details on how to configure ToS, see the Example Configuring a Negotiated L2TPv3 Session for Local HDLC Switching section.

Keepalive

The keepalive mechanism for L2TPv3 extends only to the endpoints of the tunneling protocol. L2TP has a reliable control message delivery mechanism that serves as the basis for the keepalive mechanism. The keepalive mechanism consists of an exchange of L2TP hello messages.

If a keepalive mechanism is required, the control plane is used, although it may not be used to bring up sessions. You can configure sessions manually.

In the case of static L2TPv3 sessions, a control channel between the two L2TP peers is negotiated through the exchange of start control channel request (SCCRQ), SCCRP, and SCCCN control messages. The control channel is responsible for maintaining only the keepalive mechanism through the exchange of hello messages.

The interval between hello messages is configurable per control channel. If one peer detects that the other peer has gone down through the keepalive mechanism, it sends a StopCCN control message and then notifies all the pseudowires to the peer about the event. This notification results in the teardown of both manually configured and dynamic sessions.

MTU Handling

It is important that you configure a Maximum Transmission Unit (MTU) appropriate for each L2TPv3 tunneled link. The configured MTU size ensures the following:

  • The lengths of the tunneled Layer 2 frames fall below the MTU of the destination attachment circuit.
  • The tunneled packets are not fragmented, which forces the receiving PE to reassemble them.

L2TPv3 handles the MTU as follows:

  • The default behavior is to fragment packets that are larger than the session MTU.
  • If you enable the ip dfbit set command in the pseudowire class, the default MTU behavior changes so that any packets that cannot fit within the tunnel MTU are dropped.
  • If you enable the ip pmtu command in the pseudowire class, the L2TPv3 control channel participates in the path MTU (PMTU) discovery.

If you enable this feature, the following processing is performed:

  • Internet Control Message Protocol (ICMP) unreachable messages sent back to the L2TPv3 device are deciphered and the tunnel MTU is updated accordingly. To receive ICMP unreachable messages for fragmentation errors, the Don’t Fragment (DF) bit in the tunnel header is either set according to the DF bit value received from the CE device or set statically if the ip dfbit set option is enabled. The tunnel MTU is periodically reset to the default value based on a periodic timer.
  • ICMP unreachable messages are sent back to the clients on the CE side. ICMP unreachable messages are sent to the CE whenever IP packets arrive on the CE-PE interface and have a packet size greater than the tunnel MTU. A Layer 2 header calculation is performed before the ICMP unreachable message is sent to the CE.

L2TPv3 Control Message Hashing

The L2TPv3 Control Message Hashing feature introduces a new and more secure authentication system that replaces the CHAP-like authentication system inherited from L2TPv2, which uses the Challenge and Challenge Response AV pairs in the SCCRQ, SCCRP, and SCCCN messages. The L2TPv3 Control Message Hashing feature incorporates an optional authentication or integrity check for all control messages.

The per-message authentication introduced by the L2TPv3 Control Message Hashing feature is designed to:

  • Perform a mutual authentication between L2TP nodes.
  • Check integrity of all control messages.
  • Guard against control message spoofing and replay attacks that would otherwise be trivial to mount against the network.

The new authentication method uses the following:

  • A computed, one-way hash over the header and body of the L2TP control message
  • A preconfigured, shared secret that must be defined on the communicating L2TP nodes
  • A local and remote random value exchanged using the Nonce AV pairs

Received control messages that lack any of the required security elements are dropped.

L2TPv3 control message integrity checking is a unidirectional mechanism that does not require the configuration of a shared secret. If integrity checking is enabled on the local PE device, control messages are sent with the message digest calculated without the shared secret or Nonce AV pairs and are verified by the remote PE device. If verification fails, the remote PE device drops the control message.

Enabling the L2TPv3 Control Message Hashing feature will impact performance during control channel and session establishment because additional digest calculation of the full message content is required for each sent and received control message. This is an expected trade-off for the additional security provided by this feature. In addition, network congestion may occur if the receive window size is too small. If the L2TPv3 Control Message Hashing feature is enabled, message digest validation must be enabled. Message digest validation deactivates the data path received sequence number update and restricts the minimum local receive window size to 35.

You may choose to configure control channel authentication or control message integrity checking. Control channel authentication requires participation by both peers and a shared secret must be configured on both devices. Control message integrity check is unidirectional and requires configuration on only one of the peers.

L2TPv3 Control Message Rate Limiting

The L2TPv3 Control Message Rate Limiting feature was introduced to counter the possibility of a denial-of-service (DoS) attack on a device running L2TPv3. The L2TPv3 Control Message Rate Limiting feature limits the rate at which SCCRQ control packets arriving at the PE that terminates the L2TPv3 tunnel can be processed. SCCRQ control packets initiate the process of bringing up the L2TPv3 tunnel and require a large amount of control plane resources of the PE device.

No configuration is required for the L2TPv3 Control Message Rate Limiting feature. This feature automatically runs in the background in supported releases.

L2TPv3 Digest Secret Graceful Switchover

Authentication of L2TPv3 control channel messages occurs using a password that is configured on all participating peer PE devices. Before the introduction of this feature, changing this password required removing of the old password from the configuration before adding the new password, causing an interruption in L2TPv3 services. The authentication password must be updated on all peer PE devices, which are often at different physical locations. It is difficult for all peer PE devices to be updated with the new password simultaneously to minimize interruptions in L2TPv3 services.

The L2TPv3 Digest Secret Graceful Switchover feature allows the password used to authenticate L2TPv3 control channel messages to be changed without tearing down the established L2TPv3 tunnels. This feature works only for authentication passwords configured with the L2TPv3 Control Message Hashing feature. Authentication passwords configured with the older, CHAP-like authentication system cannot be updated without tearing down L2TPv3 tunnels.

The L2TPv3 Digest Secret Graceful Switchover feature allows two control channel passwords to be configured simultaneously, so a new control channel password can be enabled without first removing the old password. Established tunnels are rapidly updated with the new password, but continue to use the old password until it is removed from the configuration. This allows authentication to continue normally with peer PE devices that have not yet been updated to use the new password. After all peer PE devices are configured with the new password, the old password can be removed from the configuration.

During the period when both a new and an old password are configured, authentication will occur only with the new password if the attempt to authenticate using the old password fails.

L2TPv3 Pseudowire

The pseudowire class configuration procedure creates a configuration template for the pseudowire. Use this template or class to configure session-level parameters for L2TPv3 sessions that are used to transport attachment circuit traffic over the pseudowire.

The pseudowire configuration specifies the characteristics of the L2TPv3 signaling mechanism, including the data encapsulation type, the control protocol, sequencing, Layer 3 fragmentation, payload-specific options, and IP properties. The setting that determines whether signaling is used to set up the pseudowire is also included.

If you specify the encapsulation l2tpv3 command, you cannot remove it by using the no encapsulation l2tpv3 command. You also cannot change the command setting by using the encapsulation mpls command. These methods result in the following error message:

Encapsulation changes are not allowed on an existing pw-class.

To remove the command, you must delete the pseudowire by using the no pseudowire-class command. To change the type of encapsulation, remove the pseudowire by using the no pseudowire-class command, reestablish the pseudowire, and specify the new encapsulation type.

Manual Clearing of L2TPv3 Tunnels

This feature lets you clear L2TPv3 tunnels manually. Before the introduction of this feature, there was no provision to clear a specific L2TPv3 tunnel manually. This functionality provides users more control over an L2TPv3 network.

L2TPv3 Tunnel Management

New and enhanced commands have been introduced to facilitate the management and diagnosis of problems with xconnect configurations. No specific configuration tasks are associated with these commands.

  • debug vpdn--The output of this command includes authentication failure messages.
  • show l2tun session--The hostname keyword allows the peer hostname to be displayed in the output.
  • show l2tun tunnel--The authentication keyword allows the display of global information about L2TP control channel authentication AV pairs.
  • show xconnect--The output of this command displays information about xconnect attachment circuits and pseudowires. This command also provides a sortable, single point of reference for information about all xconnect configurations.
  • xconnect logging pseudowire status--This command enables syslog reporting of pseudowire status events.

For information about these Cisco IOS commands, go to the Command Lookup Tool at http:/​/​tools.cisco.com/​Support/​CLILookup or to the Cisco IOS Master Commands List, All Releases.

L2TPv3 Protocol Demultiplexing

The L2TPv3 Protocol Demultiplexing feature introduces the ability to provide native IPv6 support by utilizing a specialized IPv6 network to offload IPv6 traffic from the IPv4 network. The IPv6 traffic is tunneled to the IPv6 network transparently by using L2TPv3 pseudowires without affecting the configuration of the CE devices. IPv4 traffic is routed as usual within the IPv4 network, maintaining the existing performance and reliability of the IPv4 network.

The IPv4 PE devices must be configured to demultiplex the incoming IPv6 traffic from IPv4 traffic. The PE devices facing the IPv6 network do not require the IPv6 configuration. The configuration of the IPv6 network is beyond the scope of this document. For more information on configuring an IPv6 network, see the IPv6 Configuration Guide.

L2TPv3 Custom Ethertype for Dot1q and QinQ Encapsulations

The L2TPv3 Custom Ethertype for Dot1q and QinQ Encapsulations feature lets you configure an Ethertype other than 0x8100 on Gigabit Ethernet interfaces with the QinQ or Dot1Q encapsulation. You can set the custom Ethertype to 0x9100, 0x9200, or 0x88A8. This allows interoperability in a multivendor Gigabit Ethernet environment.

HDLC over L2TPv3

HDLC for Layer 2 Data Encapsulation provides encapsulation of port-to-port Layer 2 traffic. All HDLC traffic including IPv4, IPv6, and non-IP packet, such as IS-IS, is tunneled over L2TPv3. HDLC does not support interworking mode.


Note


L2TPv3 supports the IPv4 tunnel only for HDLC. The IPv4 tunnel supports IPv4 and IPv6 packets.


L2TPv3 Benefits

Simplifies Deployment of VPNs

L2TPv3 is an industry-standard Layer 2 tunneling protocol that ensures interoperability among vendors, thus increasing customer flexibility and service availability.

Omits the Need for MPLS

Service providers need not deploy Multiprotocol Label Switching (MPLS) in the core IP backbone to set up VPNs using L2TPv3 over the IP backbone, resulting in operational savings and increased revenue.

Supports Layer 2 Tunneling over IP for Any Payload

L2TPv3 provides enhancements to L2TP to support Layer 2 tunneling of any payload over an IP core network. L2TPv3 defines the base L2TP protocol as being separate from the Layer 2 payload that is tunneled.

Other Benefits

  • Provides cookies for authentication
  • Provides session state updates and multiple sessions
  • Supports interworking (Ethernet-VLAN, Ethernet-QinQ, and VLAN-QinQ)

Supported L2TPv3 Payloads


Note


Each L2TPv3 tunneled packet includes the entire Layer 2 frame of the payloads described in this section. If sequencing is required (see the Sequencing section), a Layer 2-specific sublayer (see the Pseudowire Control Encapsulation section) is included in the L2TPv3 header to provide the Sequence Number field.


Ethernet

An Ethernet frame arriving at a PE device is simply encapsulated in its entirety with an L2TP data header. At the other end, a received L2TP data packet is stripped of its L2TP data header. The payload, an Ethernet frame, is then forwarded to the appropriate attachment circuit.

Because the L2TPv3 tunneling protocol serves essentially as a bridge, it need not examine any part of an Ethernet frame. Any Ethernet frame received on an interface is tunneled, and any L2TP-tunneled Ethernet frame is forwarded out of the interface.


Note


Because of the way in which L2TPv3 handles Ethernet frames, an Ethernet interface must be configured to promiscuous mode to capture all traffic received on the Ethernet segment attached to the device. All frames are tunneled through the L2TP pseudowire.


VLAN

L2TPv3 supports VLAN memberships in the following ways:

  • Port-based, in which undated Ethernet frames are received
  • VLAN-based, in which tagged Ethernet frames are received

In L2TPv3, Ethernet xconnect supports port-based VLAN membership and the reception of tagged Ethernet frames. A tagged Ethernet frame contains a tag header (defined in 802.1Q), which is 4 bytes long and consists of a 2-byte tag protocol identifier (TPID) field and a 2-byte tag control information (TCI) field. The TPID indicates that a TCI follows. The TCI is further broken down into the following three fields:

  • User priority field
  • Canonical format indicator (CFI)
  • A 12-bit VLAN ID (VID)

For L2TPv3, an Ethernet subinterface configured to support VLAN switching may be bound to an xconnect service so that all Ethernet traffic, tagged with a VID specified on the subinterface, is tunneled to another PE. The VLAN Ethernet frames are forwarded in their entirety. The receiving PE may rewrite the VID of the tunneled traffic to another value before forwarding the traffic onto an attachment circuit.

To successfully rewrite VLANs, it may be necessary to disable the Spanning Tree Protocol (STP). This can be done on a per-VLAN basis by using the no spanning-tree vlan command.


Note


Because of the way in which L2TPv3 handles VLAN packets, the Ethernet interface must be configured in promiscuous mode to capture all traffic received on the Ethernet segment attached to the device. All frames are tunneled through the L2TP pseudowire.


IPv6 Protocol Demultiplexing

Upgrading a service provider network to support IPv6 is a long and expensive process. As an interim solution, the Protocol Demultiplexing for L2TPv3 feature introduces the ability to provide native IPv6 support by setting up a specialized IPv6 network and offloading IPv6 traffic from the IPv4 network. IPv6 traffic is tunneled transparently to the IPv6 network using L2TPv3 pseudowires without affecting the configuration of the CE devices. IPv4 traffic is routed as usual within the IPv4 network, maintaining the existing performance and reliability of the IPv4 network.

The figure below shows a network deployment that offloads IPv6 traffic from the IPv4 network to a specialized IPv6 network. The PE devices demultiplex the IPv6 traffic from the IPv4 traffic. IPv6 traffic is routed to the IPv6 network over an L2TPv3 pseudowire, while IPv4 traffic is routed normally. The IPv4 PE devices must be configured to demultiplex the incoming IPv6 traffic from the IPv4 traffic. The PE devices facing the IPv6 network do not require the IPv6 configuration.

Figure 5. Protocol Demultiplexing of IPv6 Traffic from IPv4 Traffic

If no IP address is configured, the protocol demultiplexing configuration is rejected. If an IP address is configured, the xconnect command configuration is rejected unless protocol demultiplexing is enabled in xconnect configuration mode before exiting that mode. If an IP address is configured with an xconnect command configuration and protocol demultiplexing is enabled, the IP address cannot be removed. To change or remove the configured IP address, the xconnect command configuration must first be disabled.

The table below shows the valid combinations of configurations.

Table 2 Valid Configuration Scenarios

Scenario

IP Address

xconnect Configuration

Protocol Demultiplexing Configuration

Routing

Yes

No

--

L2VPN

No

Yes

No

IPv6 Protocol Demultiplexing

Yes

Yes

Yes

Performance Impact of L2TPv3 on Cisco ASR 1000 Series Routers

L2TPv3 supports the following maximum number of attachment circuits and tunnels:

  • First-generation Cisco ASR 1000 Series Route Processor (RP1) with Embedded Services Processor 10 (ESP10)
    • Attachment circuits for Ethernet: 8000 per system in a typical user environment. This includes 4000 per port and 8000 per SPA.
    • L2TPv3 tunnels: 1000 (in a typical user environment) and 2000 (maximum).
  • Second-generation Cisco ASR 1000 Series Route Processor (RP2) with Embedded Services Processor 20 (ESP20)
    • Attachment circuits for Ethernet: 16,000 per system in a typical user environment. This includes 4000 per port and 8000 per SPA.
    • L2TPv3 tunnels: 2000 (in a typical user environment) and 4000 (maximum).

L2TPv3 adds tunnel encapsulation to TCP packets, which can cause fragmentation of big packets (packet size larger than the session MTU). Consider a scenario where a big TCP packet is followed by a small TCP packet (packet size smaller than the session MTU). After L2TPv3 encapsulation, the encapsulated big TCP packet will be fragmented, but the encapsulated small TCP packet will not be fragmented. On the Cisco ASR 1000 Series Routers, the fragmentation and reassembly of the big TCP packet requires an additional processor cycle. Because Cisco ASR 1000 Series Routers follow multithread processing, the small packet will need shorter processing time and may be forwarded ahead of the fragmented big packet. This process may result in packet sequence changes on the receiver's end.

As a workaround, you can enable the ip pmtu command to prevent the fragmentation of tunneled packets (see the "MTU Handling" section).

How to Configure Layer 2 Tunneling Protocol Version 3

Configuring L2TP Control Channel Parameters

After you enter L2TP class configuration mode, you can configure L2TP control channel parameters in any order. If you have multiple authentication requirements, you can configure multiple sets of L2TP class control channel parameters with different L2TP class names. However, only one set of parameters can be applied to a connection between any pair of IP addresses.

Configuring L2TP Control Channel Timing Parameters

The following L2TP control channel timing parameters can be configured in L2TP class configuration mode:

  • Packet size of the receive window used for the control channel
  • Retransmission parameters used for control messages
  • Timeout parameters used for the control channel

This task configures a set of timing control channel parameters in an L2TP class. All of the timing control channel parameter configurations are optional and may be configured in any order. If these parameters are not configured, default values are applied.

SUMMARY STEPS

    1.    enable

    2.    configure terminal

    3.    l2tp-class [l2tp-class-name]

    4.    retransmit {initial retries initial-retries | retries retries | timeout {max | min} timeout}

    5.    timeout setup seconds

    6.    exit


DETAILED STEPS
     Command or ActionPurpose
    Step 1 enable


    Example:
    Device> enable
     

    Enables privileged EXEC mode.

    • Enter your password if prompted.
     
    Step 2 configure terminal


    Example:
    Device# configure terminal
     

    Enters global configuration mode.

     
    Step 3 l2tp-class [l2tp-class-name]


    Example:
    Device(config)# l2tp-class class1
     

    Specifies the L2TP class name and enters L2TP class configuration mode.

    • The l2tp-class-name argument is optional. However, to configure multiple L2TP classes, you must specify a unique l2tp-class-name for each one.
     
    Step 4 retransmit {initial retries initial-retries | retries retries | timeout {max | min} timeout}


    Example:
    Device(config-l2tp-class)# retransmit retries 10
     

    (Optional) Configures parameters that affect the retransmission of control packets.

    • initial retries—Specifies how many SCCRQs are resent before giving up on the session. Valid values for the initial-retries argument range from 1 to 1000. The default value is 2.
    • retries—Specifies how many retransmission cycles occur before determining that the peer PE device is not responding. Valid values for the retries argument range from 1 to 1000. The default value is 15.
    • timeout {max | min}—Specifies maximum and minimum retransmission intervals (in seconds) for resending control packets. Valid values for the timeout argument range from 1 to 8. The default maximum interval is 8. The default minimum interval is 1.
     
    Step 5 timeout setup seconds


    Example:
    Device(config-l2tp-class)# timeout setup 400
     

    (Optional) Configures the amount of time, in seconds, allowed to set up a control channel.

    • Valid values for the seconds argument range from 60 to 6000. The default value is 300.
     
    Step 6 exit


    Example:
    Device(config-l2tp-class)# exit
     

    Exits L2TP class configuration mode.

     

    Configuring L2TPv3 Control Channel Authentication Parameters

    Configuring Authentication for the L2TP Control Channel

    The L2TP control channel method of authentication is the older, CHAP-like authentication system inherited from L2TPv2.

    The following L2TP control channel authentication parameters can be configured in L2TP class configuration mode:

    • Authentication for the L2TP control channel
    • Password used for L2TP control channel authentication
    • Local hostname used for authenticating the control channel

    This task configures a set of authentication control channel parameters in an L2TP class. All of the authentication control channel parameter configurations are optional and may be configured in any order. If these parameters are not configured, default values are applied.

    SUMMARY STEPS

      1.    enable

      2.    configure terminal

      3.    l2tp-class [l2tp-class-name]

      4.    authentication

      5.    password [0 | 7] password

      6.    hostname name

      7.    exit


    DETAILED STEPS
       Command or ActionPurpose
      Step 1 enable


      Example:
      Device> enable
       

      Enables privileged EXEC mode.

      • Enter your password if prompted.
       
      Step 2 configure terminal


      Example:
      Device# configure terminal
       

      Enters global configuration mode.

       
      Step 3 l2tp-class [l2tp-class-name]


      Example:
      Device(config)# l2tp-class class1
       

      Specifies the L2TP class name and enters L2TP class configuration mode.

      • The l2tp-class-name argument is optional. However, to configure multiple L2TP classes, you must specify a unique l2tp-class-name for each one.
       
      Step 4 authentication


      Example:
      Device(config-l2tp-class)# authentication
       

      (Optional) Enables authentication for the control channel between PE devices.

       
      Step 5 password [0 | 7] password


      Example:
      Device(config-l2tp-class)# password cisco
       

      (Optional) Configures the password used for control channel authentication.

      • [0 | 7]—(Optional) Specifies the input format of the shared secret. The default value is 0.
        • 0—Specifies that a plain-text secret is entered.
        • 7—Specifies that an encrypted secret is entered.
      • password—Defines the shared password between peer devices.
       
      Step 6 hostname name


      Example:
      Device(config-l2tp-class)# hostname yb2
       

      (Optional) Specifies a hostname used to identify the device during L2TP control channel authentication.

      • If you do not use this command, the default hostname of the device is used.
       
      Step 7 exit


      Example:
      Device(config-l2tp-class)# exit
       

      Exits L2TP class configuration mode.

       
      Configuring L2TPv3 Control Message Hashing

      This task configures L2TPv3 Control Message Hashing feature for an L2TP class.

      SUMMARY STEPS

        1.    enable

        2.    configure terminal

        3.    l2tp-class [l2tp-class-name]

        4.    digest [secret [0 | 7] password] [hash {md5 | sha}]

        5.    digest check

        6.    hidden

        7.    exit


      DETAILED STEPS
         Command or ActionPurpose
        Step 1 enable


        Example:
        Device> enable
         

        Enables privileged EXEC mode.

        • Enter your password if prompted.
         
        Step 2 configure terminal


        Example:
        Device# configure terminal
         

        Enters global configuration mode.

         
        Step 3 l2tp-class [l2tp-class-name]


        Example:
        Device(config)# l2tp-class class1
         

        Specifies the L2TP class name and enters L2TP class configuration mode.

        • The l2tp-class-name argument is optional. However, to configure multiple L2TP classes, you must specify a unique l2tp-class-name for each one.
         
        Step 4 digest [secret [0 | 7] password] [hash {md5 | sha}]


        Example:
        Device(config-l2tp-class)# digest secret cisco hash sha
         

        (Optional) Enables L2TPv3 control channel authentication or integrity checking.

        • secret—(Optional) Enables L2TPv3 control channel authentication.
        Note   

        If the digest command is issued without the secret keyword option, L2TPv3 integrity checking is enabled.

        • [0 | 7]—Specifies the input format of the shared secret. The default value is 0.
          • 0—Specifies that a plain-text secret is entered.
          • 7—Specifies that an encrypted secret is entered.
        • password—Defines the shared secret between peer devices. The value entered for the password argument must be in the format that matches the input format specified by the [0 | 7] keyword option.
        • hash {md5 | sha}—(Optional) Specifies the hash function to be used in per-message digest calculations.
          • md5—Specifies HMAC-MD5 hashing.
          • sha—Specifies HMAC-SHA-1 hashing.

        The default hash function is md5.

         
        Step 5 digest check


        Example:
        Device(config-l2tp-class)# digest check
         

        (Optional) Enables the validation of the message digest in received control messages.

        • Validation of the message digest is enabled by default.
        Note   

        Validation of the message digest cannot be disabled if authentication has been enabled using the digest secret command. If authentication has not been configured with the digest secret command, the digest check can be disabled to increase performance.

         
        Step 6 hidden


        Example:
        Device(config-l2tp-class)# hidden
         

        (Optional) Enables AV pair hiding when sending control messages to an L2TPv3 peer.

        • AV pair hiding is disabled by default.
        • Only the hiding of the cookie AV pair is supported.
        • If a cookie is configured in L2TP class configuration mode (see the section "Manually Configuring L2TPv3 Session Parameters"), enabling AV pair hiding causes that cookie to be sent to the peer as a hidden AV pair using the password configured with the digest secret command.
        Note   

        AV pair hiding is enabled only if authentication has been enabled using the digest secret command, and no other authentication method is configured.

         
        Step 7 exit


        Example:
        Device(config-l2tp-class)# exit
         

        Exits L2TP class configuration mode.

         
        Configuring L2TPv3 Digest Secret Graceful Switchover

        Perform this task to make the transition from an old L2TPv3 control channel authentication password to a new L2TPv3 control channel authentication password without disrupting established L2TPv3 tunnels.

        Before You Begin

        Before performing this task, you must enable control channel authentication as documented in the Configuring L2TPv3 Control Message Hashing task.


        Note


        This task is not compatible with authentication passwords configured with the older, CHAP-like control channel authentication system.


        SUMMARY STEPS

          1.    enable

          2.    configure terminal

          3.    l2tp-class l2tp-class-name

          4.    digest [secret [0 | 7] password] [hash {md5 | sha}]

          5.    end

          6.    show l2tun tunnel all

          7.    configure terminal

          8.    l2tp-class [l2tp-class-name]

          9.    no digest [secret [0 | 7] password [hash {md5 | sha}]

          10.    end

          11.    show l2tun tunnel all


        DETAILED STEPS
           Command or ActionPurpose
          Step 1 enable


          Example:
          Device> enable
           

          Enables privileged EXEC mode.

          • Enter your password if prompted.
           
          Step 2 configure terminal


          Example:
          Device# configure terminal
           

          Enters global configuration mode.

           
          Step 3 l2tp-class l2tp-class-name


          Example:
          Device(config)# l2tp-class class1
           

          Specifies the L2TP class name and enters L2TP class configuration mode.

           
          Step 4 digest [secret [0 | 7] password] [hash {md5 | sha}]


          Example:
          Device(config-l2tp-class)# digest secret cisco2 hash sha
           

          Configures a new password to be used in L2TPv3 control channel authentication.

          • A maximum of two passwords may be configured at any time.
          Note   

          Authentication will now occur using both the old and new passwords.

           
          Step 5 end


          Example:
          Device(config-l2tp-class)# end
           

          Ends your configuration session by exiting to privileged EXEC mode.

           
          Step 6 show l2tun tunnel all


          Example:
          Device# show l2tun tunnel all
           

          (Optional) Displays the current state of Layer 2 tunnels and information about configured tunnels, including local and remote L2TP hostnames, aggregate packet counts, and control channel information.

          • Tunnels should be updated with the new control channel authentication password within a matter of seconds. If a tunnel does not update to show that two secrets are configured after several minutes have passed, the tunnel can be cleared manually and a defect report should be filed with the Cisco Technical Assistance Center (TAC). To clear an L2TPv3 tunnel manually, perform the task described in the section “Manually Clearing L2TPv3 Tunnels. ”
          Note   

          Issue this command to determine whether any tunnel is using the new password for control channel authentication. The output displayed for each tunnel in the specified L2TP class should show that two secrets are configured.

           
          Step 7 configure terminal


          Example:
          Device# configure terminal
           

          Enters global configuration mode.

           
          Step 8 l2tp-class [l2tp-class-name]


          Example:
          Device(config)# l2tp-class class1
           

          Specifies the L2TP class name and enters L2TP class configuration mode.

          • The l2tp-class-name argument is optional. However, to configure multiple L2TP classes, you must specify a unique l2tp-class-name for each one.
           
          Step 9 no digest [secret [0 | 7] password [hash {md5 | sha}]


          Example:
          Device(config-l2tp-class)# no digest secret cisco hash sha
           

          Removes the old password used in L2TPv3 control channel authentication.

          Note   

          Do not remove the old password until all peer PE devices have been updated with the new password.

           
          Step 10 end


          Example:
          Device(config-l2tp-class)# end
           

          Ends your configuration session by exiting to privileged EXEC mode.

           
          Step 11 show l2tun tunnel all


          Example:
          Device# show l2tun tunnel all
           

          (Optional) Displays the current state of Layer 2 tunnels and information about configured tunnels, including local and remote L2TP hostnames, aggregate packet counts, and control channel information.

          • Tunnels should no longer be using the old control channel authentication password. If a tunnel does not update to show that only one secret is configured after several minutes have passed, that tunnel can be cleared manually and a defect report should be filed with TAC. To clear an L2TPv3 tunnel manually, perform the task described in the section “Manually Clearing L2TPv3 Tunnels.”
          Note   

          Issue this command to ensure that all tunnels are using only the new password for control channel authentication. The output displayed for each tunnel in the specified L2TP class should show that one secret is configured.

           

          Configuring L2TP Control Channel Maintenance Parameters

          The L2TP hello packet keepalive interval control channel maintenance parameter can be configured in L2TP class configuration mode.

          This task configures the interval used for hello messages in an L2TP class. This control channel parameter configuration is optional. If this parameter is not configured, the default value is applied.

          SUMMARY STEPS

            1.    enable

            2.    configure terminal

            3.    l2tp-class [l2tp-class-name]

            4.    hello interval

            5.    exit


          DETAILED STEPS
             Command or ActionPurpose
            Step 1 enable


            Example:
            Device> enable
             

            Enables privileged EXEC mode.

            • Enter your password if prompted.
             
            Step 2 configure terminal


            Example:
            Device# configure terminal
             

            Enters global configuration mode.

             
            Step 3 l2tp-class [l2tp-class-name]


            Example:
            Device(config)# l2tp-class class1
             

            Specifies the L2TP class name and enters L2TP class configuration mode.

            • The l2tp-class-name argument is optional. However, to configure multiple L2TP classes, you must specify a unique l2tp-class-name for each one.
             
            Step 4 hello interval


            Example:
            Device(config-l2tp-class)# hello 100
             

            (Optional) Specifies the exchange interval (in seconds) used between L2TP hello packets.

            • Valid values for the interval argument range from 0 to 1000. The default value is 60.
             
            Step 5 exit


            Example:
            Device(config-l2tp-class)# exit
             

            Exits L2TP class configuration mode.

             

            Configuring the L2TPv3 Pseudowire

            Perform this task to configure the L2TPv3 pseudowire.

            SUMMARY STEPS

              1.    enable

              2.    configure terminal

              3.    pseudowire-class [pw-class-name]

              4.    encapsulation l2tpv3

              5.    protocol {l2tpv3 | none} [l2tp-class-name]

              6.    ip local interface interface-name

              7.    ip pmtu

              8.    ip tos {value value | reflect}

              9.    ip dfbit set

              10.    ip ttl value

              11.    ip protocol {l2tp | protocol-number}

              12.    sequencing {transmit | receive | both}

              13.    exit


            DETAILED STEPS
               Command or ActionPurpose
              Step 1 enable


              Example:
              Device> enable
               

              Enables privileged EXEC mode.

              • Enter your password if prompted.
               
              Step 2 configure terminal


              Example:
              Device# configure terminal
               

              Enters global configuration mode.

               
              Step 3 pseudowire-class [pw-class-name]


              Example:
              Device(config)# pseudowire-class etherpw
               

              Enters pseudowire class configuration mode and optionally specifies the name of the L2TP pseudowire class.

               
              Step 4 encapsulation l2tpv3


              Example:
              Device(config-pw)# encapsulation l2tpv3
               

              Specifies that L2TPv3 is used as the data encapsulation method to tunnel IP traffic.

               
              Step 5 protocol {l2tpv3 | none} [l2tp-class-name]


              Example:
              Device(config-pw)# protocol l2tpv3 class1
               

              (Optional) Specifies the L2TPv3 signaling protocol to be used to manage the pseudowires created with the control channel parameters in the specified L2TP class (see the section "Configuring L2TP Control Channel Parameters").

              • If the l2tp-class-name argument is not specified, the default values for L2TP control channel parameters are used. The default protocol option is l2tpv3.
              • If you do not want to use signaling in the L2TPv3 sessions created with this pseudowire class, enter protocol none.
               
              Step 6 ip local interface interface-name


              Example:
              Device(config-pw)# ip local interface e0/0
               

              Specifies the PE device interface whose IP address is to be used as the source IP address for sending tunneled packets.

              • The same or a different local interface name can be used for each of the pseudowire classes configured between a pair of PE devices.
              Note   

              This command must be configured for pseudowire-class configurations using L2TPv3 as the data encapsulation method.

               
              Step 7 ip pmtu


              Example:
              Device(config-pw)# ip pmtu
               

              (Optional) Enables the discovery of the PMTU for tunneled traffic and helps fragmentation.

              • This command enables the processing of ICMP unreachable messages that indicate fragmentation errors in the backbone network that carries L2TPv3 session traffic. Also, this command enables MTU checking for IP packets sent into the session and that have the DF bit set. Any IP packet larger than the MTU is dropped and an ICMP unreachable message is sent. MTU discovery is disabled by default.
              Note   

              The ip pmtu command is not supported if you disabled signaling with the protocol none command in Step 5.

              • This command must be enabled in the pseudowire class configuration to enable fragmentation of IP packets before the data enters the pseudowire.
              Note   

              To enable fragmentation of IP packets before the data enters the pseudowire, Cisco recommends that you also enter the ip dfbit set command in pseudowire class configuration mode. This allows the PMTU to be obtained more rapidly.

              Note   

              When the ip pmtu command is enabled, the DF bit is copied from the inner IP header to the outer IP header. If no IP header is found inside the Layer 2 frame, the DF bit in the outer IP is set to 0.

               
              Step 8 ip tos {value value | reflect}


              Example:
              Device(config-pw)# ip tos reflect
               

              (Optional) Configures the value of the ToS byte in IP headers of tunneled packets, or reflects the ToS byte value from the inner IP header.

              • Valid values for the value argument range from 0 to 255. The default ToS byte value is 0.
               
              Step 9 ip dfbit set


              Example:
              Device(config-pw)# ip dfbit set
               
              (Optional) Configures the value of the DF bit in the outer headers of tunneled packets.
              • Use this command if (for performance reasons) you do not want reassembly of tunneled packets on the peer PE device.
              • This command is disabled by default.
               
              Step 10 ip ttl value


              Example:
              Device(config-pw)# ip ttl 100
               

              (Optional) Configures the value of the time to live (TTL) byte in the IP headers of tunneled packets.

              • Valid values for the value argument range from 1 to 255. The default TTL byte value is 255.
               
              Step 11 ip protocol {l2tp | protocol-number}


              Example:
              Device(config-pw)# ip protocol l2tp
               

              (Optional) Configures the IP protocol to be used for tunneling packets.

               
              Step 12 sequencing {transmit | receive | both}


              Example:
              Device(config-pw)# sequencing both
               

              (Optional) Specifies the direction in which sequencing of data packets in a pseudowire is enabled:

              • transmit—Updates the Sequence Number field in the headers of data packets sent over the pseudowire according to the data encapsulation method that is used.
              • receive—Keeps the Sequence Number field in the headers of data packets received over the pseudowire. Out-of-order packets are dropped.
              • both—Enables both the transmit and receive options.
               
              Step 13 exit


              Example:
              Device(config-pw)# exit
               

              Exits pseudowire class configuration mode.

               

              Configuring the Xconnect Attachment Circuit

              The virtual circuit identifier that you configure creates the binding between a pseudowire configured on a PE device and an attachment circuit in a CE device. The virtual circuit identifier configured on the PE device at one end of the L2TPv3 control channel must also be configured on the peer PE device at the other end.

              SUMMARY STEPS

                1.    enable

                2.    configure terminal

                3.    interface type slot / port

                4.    xconnect peer-ip-address vcid pseudowire-parameters [sequencing {transmit | receive | both}]

                5.    exit


              DETAILED STEPS
                 Command or ActionPurpose
                Step 1 enable


                Example:
                Device> enable
                 

                Enables privileged EXEC mode.

                • Enter your password if prompted.
                 
                Step 2 configure terminal


                Example:
                Device# configure terminal
                 

                Enters global configuration mode.

                 
                Step 3 interface type slot / port


                Example:
                Device(config)# interface ethernet 0/0
                 

                Specifies the interface by type (for example, Ethernet), slot, and port number, and enters interface configuration mode.

                 
                Step 4 xconnect peer-ip-address vcid pseudowire-parameters [sequencing {transmit | receive | both}]


                Example:
                Device(config-if)# xconnect 10.0.3.201 123 pw-class vlan-xconnect
                 

                Specifies the IP address of the peer PE device and the 32-bit virtual circuit identifier shared between the PE at each end of the control channel.

                • The peer device ID (IP address) and virtual circuit ID must be a unique combination on the device.
                • At least one of the following pseudowire class parameters must be configured for the pseudowire-parameters argument:
                  • encapsulation {l2tpv3 [manual] | mpls}—Specifies the tunneling method used to encapsulate data in the pseudowire:
                    • l2tpv3—L2TPv3 is the tunneling method to be used.
                    • manual—(Optional) No signaling is to be used in the L2TPv3 control channel. This command places the device in xconnect configuration mode for the manual configuration of L2TPv3 parameters for the attachment circuit.
                    • mpls—MPLS is the tunneling method to be used.
                • pw-class {pw-class-name}—The pseudowire class configuration from which the data encapsulation type (L2TPv3) is taken.
                • The optional encapsulation parameter specifies the method of pseudowire tunneling used: L2TPv3 or MPLS. Enter manual if you do not want signaling to be used in the L2TPv3 control channel. The encapsulation l2tpv3 manual keyword combination enters xconnect configuration submode. See the section "Manually Configuring L2TPv3 Session Parameters" for the other L2TPv3 commands that you must enter to complete the configuration of the L2TPv3 control channel. If you do not enter an encapsulation value, the encapsulation method entered with the password command in the Configuring the Xconnect Attachment Circuit task is used.
                • The optional pw-class parameter binds the xconnect statement to a specific pseudowire class. The pseudowire class then serves as the template configuration for all attachment circuits bound to it. Specify the pseudowire-class option if you need to configure more advanced options.
                Note   

                You must configure either the encapsulation or the pw-class option or both.

                Note   

                If you select L2TPv3 as your data encapsulation method, you must specify the pw-class keyword.

                • The optional sequencing parameter specifies whether sequencing is required for packets that are received, sent, or both received and sent.
                 
                Step 5 exit


                Example:
                Device(config-if)# exit
                 

                Exits interface configuration mode.

                 

                Manually Configuring L2TPv3 Session Parameters

                When you bind an attachment circuit to an L2TPv3 pseudowire for the xconnect service by using the xconnect l2tpv3 manual command (see the section "Configuring the Xconnect Attachment Circuit") because you do not want signaling, you must configure L2TP-specific parameters to complete the L2TPv3 control channel configuration.

                SUMMARY STEPS

                  1.    enable

                  2.    configure terminal

                  3.    interface type slot / port

                  4.    xconnect peer-ip-address vc-id encapsulation l2tpv3 manual pw-class pw-class-name

                  5.    l2tp id local-session-id remote-session-id

                  6.    l2tp cookie local size low-value [high-value]

                  7.    l2tp cookie remote size low-value [high-value]

                  8.    l2tp hello l2tp-class-name

                  9.    exit

                  10.    exit


                DETAILED STEPS
                   Command or ActionPurpose
                  Step 1 enable


                  Example:
                  Device> enable
                   

                  Enables privileged EXEC mode.

                  • Enter your password if prompted.
                   
                  Step 2 configure terminal


                  Example:
                  Device# configure terminal
                   

                  Enters global configuration mode.

                   
                  Step 3 interface type slot / port


                  Example:
                  Device(config)# interface ethernet 0/0
                   

                  Specifies the interface by type (for example, Ethernet), slot, and port number, and enters interface configuration mode.

                   
                  Step 4 xconnect peer-ip-address vc-id encapsulation l2tpv3 manual pw-class pw-class-name


                  Example:
                  Device(config-if)# xconnect 10.0.3.201 123 encapsulation l2tpv3 manual pw-class vlan-xconnect
                   

                  Specifies the IP address of the peer PE device and the 32-bit virtual circuit identifier shared between the PE at each end of the control channel, and enters xconnect configuration mode.

                  • The peer device ID (IP address) and virtual circuit ID must be a unique combination on the device.
                  • The encapsulation l2tpv3 manual parameter specifies that L2TPv3 is to be used as the pseudowire tunneling method.
                  • The mandatory pw-class pw-class-name keyword and argument combination specifies the pseudowire class configuration from which the data encapsulation type (L2TPv3) is taken.
                   
                  Step 5 l2tp id local-session-id remote-session-id


                  Example:
                  Device(config-if-xconn)# l2tp id 222 111
                   

                  Configures the identifiers for the local L2TPv3 session and for the remote L2TPv3 session on the peer PE device.

                  • This command is required to complete the attachment circuit configuration and a static L2TPv3 session configuration.
                   
                  Step 6 l2tp cookie local size low-value [high-value]


                  Example:
                  Device(config-if-xconn)# l2tp cookie local 4 54321
                   

                  (Optional) Specifies the value that the peer PE must include in the cookie field of incoming (received) L2TP packets.

                  • The size of the cookie field can be 4 or 8 bytes. If you do not enter this command, no cookie value is included in the header of L2TP packets.
                  • If you configure the cookie length in incoming packets as 8 bytes, you must specify a 4-byte high value and a 4-byte low value.
                   
                  Step 7 l2tp cookie remote size low-value [high-value]


                  Example:
                  Device(config-if-xconn)# l2tp cookie remote 4 12345
                   

                  (Optional) Specifies the value that the device includes in the cookie field of outgoing (sent) L2TP packets.

                  • The size of the cookie field can be 4 or 8 bytes. If you do not enter this command, no cookie value is included in the header of L2TP packets.
                  • If you configure the cookie length in outgoing packets as 8 bytes, you must specify a 4-byte high value and a 4-byte low value.
                   
                  Step 8 l2tp hello l2tp-class-name


                  Example:
                  Device(config-if-xconn)# l2tp hello l2tp-defaults
                   

                  (Optional) Specifies the L2TP class name to be used (see the section "Configuring L2TP Control Channel Parameters") for control channel configuration parameters, including the interval to use between hello keepalive messages.

                  Note   

                  This command assumes that there is no control plane to negotiate control channel parameters and that a control channel is to be used to provide keepalive support through an exchange of L2TP hello messages. By default, no hello messages are sent.

                   
                  Step 9 exit


                  Example:
                  Device(config-if-xconn)# exit
                   

                  Exits xconnect configuration mode.

                   
                  Step 10 exit


                  Example:
                  Device(config-if)# exit
                   

                  Exits interface configuration mode.

                   

                  Configuring Protocol Demultiplexing for L2TPv3

                  Configuring Protocol Demultiplexing for Ethernet Interfaces

                  Perform this task to configure the Protocol Demultiplexing feature on an Ethernet interface.

                  SUMMARY STEPS

                    1.    enable

                    2.    configure terminal

                    3.    interface type slot / port

                    4.    ip address ip-address mask [secondary]

                    5.    xconnect peer-ip-address vcid pw-class pw-class-name

                    6.    match protocol ipv6

                    7.    exit

                    8.    exit


                  DETAILED STEPS
                     Command or ActionPurpose
                    Step 1 enable


                    Example:
                    Device> enable
                     

                    Enables privileged EXEC mode.

                    • Enter your password if prompted.
                     
                    Step 2 configure terminal


                    Example:
                    Device# configure terminal
                     

                    Enters global configuration mode.

                     
                    Step 3 interface type slot / port


                    Example:
                    Device(config)# interface ethernet 0/1
                     

                    Specifies the interface by type, slot, and port number, and enters interface configuration mode.

                     
                    Step 4 ip address ip-address mask [secondary]


                    Example:
                    Device(config-if)# ip address 172.16.128.4
                     

                    Sets a primary or secondary IP address for an interface.

                     
                    Step 5 xconnect peer-ip-address vcid pw-class pw-class-name


                    Example:
                    Device(config-if)# xconnect 10.0.3.201 888 pw-class demux
                     

                    Specifies the IP address of the peer PE device and the 32-bit VCI shared between the PE at each end of the control channel, and enters xconnect configuration mode.

                    • The peer device ID (IP address) and virtual circuit ID must be a unique combination on the device.
                    • pw-class pw-class-name—The pseudowire class configuration from which the data encapsulation type (L2TPv3) is taken. The pw-class parameter binds the xconnect statement to a specific pseudowire class. The pseudowire class then serves as the template configuration for all attachment circuits bound to it.
                    Note   

                    The L2TPv3 session can also be provisioned manually. See the section "Manually Configuring L2TPv3 Session Parameters" for information about manually configuring the L2TPv3 session parameters.

                     
                    Step 6 match protocol ipv6


                    Example:
                    Device(config-if-xconn)# match protocol ipv6
                     

                    Enables protocol demultiplexing of IPv6 traffic.

                     
                    Step 7 exit


                    Example:
                    Device(config-if-xconn)# exit
                     

                    Exits xconnect configuration mode.

                     
                    Step 8 exit


                    Example:
                    Device(config-if)# exit
                     

                    Exits interface configuration mode.

                     

                    Configuring an L2TPv3 Custom Ethertype for Dot1q and QinQ Encapsulations

                    The L2TPv3 Custom Ethertype for dot1q and QinQ Encapsulations feature lets you configure an Ethertype other than 0x8100 on Gigabit Ethernet interfaces with QinQ or dot1Q encapsulations. You can set the custom Ethertype to 0x9100, 0x9200, or 0x88A8. To define the Ethertype field type, you use the dot1q tunneling ethertype command.

                    Perform this task to set a custom Ethertype.

                    SUMMARY STEPS

                      1.    enable

                      2.    configure terminal

                      3.    interface type number

                      4.    dot1q tunneling ethertype {0x88A8 | 0x9100 | 0x9200}

                      5.    exit


                    DETAILED STEPS
                       Command or ActionPurpose
                      Step 1 enable


                      Example:
                      Device> enable
                       

                      Enables privileged EXEC mode.

                      • Enter your password if prompted.
                       
                      Step 2 configure terminal


                      Example:
                      Device# configure terminal
                       

                      Enters global configuration mode.

                       
                      Step 3 interface type number


                      Example:
                      Device(config)# interface gigabitethernet 1/0/0
                       

                      Specifies an interface and enters interface configuration mode.

                       
                      Step 4 dot1q tunneling ethertype {0x88A8 | 0x9100 | 0x9200}


                      Example:
                      Device(config-if)# dot1q tunneling ethertype 0x9100
                       

                      Defines the Ethertype field type used by peer devices when implementing Q-in-Q VLAN tagging.

                       
                      Step 5 exit


                      Example:
                      Device(config-if)# exit
                       

                      Exits interface configuration mode.

                       

                      Configuring GEC over L2TPv3

                      Perform this task to configure Gigabit EtherChannel (GEC) over Layer 2 Tunneling Protocol Version 3 (L2TPv3).

                      SUMMARY STEPS

                        1.    enable

                        2.    configure terminal

                        3.    interface Loopback0

                        4.    ip address ip-address

                        5.    exit

                        6.    pseudowire-class [pw-class-name]

                        7.    encapsulation l2tpv3

                        8.    ip local interface interface-name

                        9.    exit

                        10.    interface port-channel channel-number

                        11.    xconnect peer-ip-address encapsulation l2tpv3 pw-class pw-class-name

                        12.    exit

                        13.    interface gigabitethernet interface-type-number

                        14.    channel-group channel-group-number

                        15.    end


                      DETAILED STEPS
                         Command or ActionPurpose
                        Step 1 enable


                        Example:
                        Device> enable
                         

                        Enables privileged EXEC mode.

                        • Enter your password if prompted.
                         
                        Step 2 configure terminal


                        Example:
                        Device# configure terminal
                         

                        Enters global configuration mode.

                         
                        Step 3 interface Loopback0


                        Example:
                        Device(config)# interface Loopback0
                         

                        Creates a loopback interface and enters interface configuration mode.

                         
                        Step 4 ip address ip-address


                        Example:
                        Device(config-if)# ip address 10.1.0.1 255.255.255.255
                         

                        Assigns an IP address to the interface.

                         
                        Step 5 exit


                        Example:
                        Device(config-if)# exit
                         

                        Exits interface configuration mode.

                         
                        Step 6 pseudowire-class [pw-class-name]


                        Example:
                        Device(config)# pseudowire-class l2tpv3
                         

                        Enters pseudowire class configuration mode and optionally specifies the name of the Layer 2 Tunneling Protocol (L2TP) pseudowire class.

                         
                        Step 7 encapsulation l2tpv3


                        Example:
                        Device(config-pw)# encapsulation l2tpv3 
                         

                        Specifies that L2TPv3 is used as the data encapsulation method to tunnel IP traffic.

                         
                        Step 8 ip local interface interface-name


                        Example:
                        Device(config-pw)# ip local interface loopback0 
                         

                        Specifies the provider edge (PE) interface whose IP address is to be used as the source IP address for sending tunneled packets.

                        • Use the same local interface name for all pseudowire classes that are configured between a pair of PE devices.
                        Note    This command must be configured for pseudowire-class configurations using L2TPv3 as the data encapsulation method.
                         
                        Step 9 exit


                        Example:
                        Device(config-pw)# exit
                         

                        Exits pseudowire class configuration mode and enters global configuration mode.

                         
                        Step 10 interface port-channel channel-number


                        Example:
                        Device# interface port-channel 1
                         

                        Defines a port channel and enters interface configuration mode.

                         
                        Step 11 xconnect peer-ip-address encapsulation l2tpv3 pw-class pw-class-name


                        Example:
                        Device(config-subif)# xconnect 10.0.3.201 1234 encapsulation l2tpv3 pw-class l2tpv3
                         

                        Specifies the IP address of the peer PE device and the 32-bit virtual circuit identifier (VCI) shared between the PE at each end of the control channel.

                        • The combination of the peer device ID and the VCI must be unique.
                        • pw-class pw-class-name—The pseudowire class configuration from which the data encapsulation type (L2TPv3) is taken. The pw-class parameter binds xconnect to a specific pseudowire class. The pseudowire class then serves as a template for all attachment circuits bound to it.
                         
                        Step 12 exit


                        Example:
                        Device(config-subif)# exit
                         

                        Exits subinterface configuration mode and enters global configuration mode.

                         
                        Step 13 interface gigabitethernet interface-type-number


                        Example:
                        Device(config)# interface gigabitEthernet 0/0/0
                         

                        Enters interface configuration mode.

                         
                        Step 14 channel-group channel-group-number


                        Example:
                        Device(config-if)# channel-group 1
                         

                        Add the interface to an EtherChannel group.

                         
                        Step 15 end


                        Example:
                        Device(config-if)# end
                         

                        Exits interface configuration mode and returns to privileged EXEC mode.

                         

                        Configuring GEC with Dot1Q

                        Perform this task to configure Gigabit EtherChannel (GEC) with VLAN over Layer 2 Tunneling Protocol Version 3 (L2TPv3).

                        SUMMARY STEPS

                          1.    enable

                          2.    configure terminal

                          3.    interface port-channel interface-number

                          4.    encapsulation dot1q vlan-id

                          5.    xconnect peer-ip-address encapsulation l2tpv3 pw-class pw-class-name

                          6.    end


                        DETAILED STEPS
                           Command or ActionPurpose
                          Step 1 enable


                          Example:
                          Device> enable
                           

                          Enables privileged EXEC mode.

                          • Enter your password if prompted.
                           
                          Step 2 configure terminal


                          Example:
                          Device# configure terminal
                           

                          Enters global configuration mode.

                           
                          Step 3 interface port-channel interface-number


                          Example:
                          Device(config)# interface port-channel 1.1
                           

                          Defines a port channel and enters subinterface configuration mode.

                           
                          Step 4 encapsulation dot1q vlan-id


                          Example:
                          Device(config-subif)# encapsulation dot1q 100 
                           

                          Specifies that dot1q is used as the data encapsulation method to tunnel IP traffic.

                           
                          Step 5 xconnect peer-ip-address encapsulation l2tpv3 pw-class pw-class-name


                          Example:
                          Device(config-subif)# xconnect 10.0.3.201 1234 encapsulation l2tpv3 pw-class l2tpv3
                           

                          Specifies the IP address of the peer provider edge (PE) device and the 32-bit virtual circuit identifier (VCI) that is shared between the PE device at each end of the control channel.

                          • The combination of the peer device ID and the VCI must be unique.
                          • pw-class pw-class-name—The pseudowire class configuration from which the data encapsulation type (L2TPv3) is taken. The pw-class parameter binds xconnect to a specific pseudowire class. The pseudowire class then serves as a template for all attachment circuits bound to it.
                           
                          Step 6 end


                          Example:
                          Device# end
                           

                          Exits subinterface configuration mode and returns to privileged EXEC mode .

                           

                          Configuring GEC with QinQ

                          Perform this task to configure Gigabit EtherChannel (GEC) with queue-in-queue (QinQ) over Layer 2 Tunneling Protocol Version 3 (L2TPv3).

                          SUMMARY STEPS

                            1.    enable

                            2.    configure terminal

                            3.    interface port-channel interface-number

                            4.    encapsulation dot1q vlan-id second-dot1q second-vlan-id

                            5.    xconnect peer-ip-address encapsulation l2tpv3 pw-class pw-class-name

                            6.    end


                          DETAILED STEPS
                             Command or ActionPurpose
                            Step 1 enable


                            Example:
                            Device> enable
                             

                            Enables privileged EXEC mode.

                            • Enter your password if prompted.
                             
                            Step 2 configure terminal


                            Example:
                            Device# configure terminal
                             

                            Enters global configuration mode.

                             
                            Step 3 interface port-channel interface-number


                            Example:
                            Device(config)# interface port-channel 1.1
                             

                            Defines the subinterface as a port channel and enters subinterface configuration mode.

                             
                            Step 4 encapsulation dot1q vlan-id second-dot1q second-vlan-id


                            Example:
                            Device(config-subif)# encapsulation dot1q 100 second-dot1q 200  
                             

                            Specifies that QinQ is used as the data encapsulation method to tunnel IP traffic.

                             
                            Step 5 xconnect peer-ip-address encapsulation l2tpv3 pw-class pw-class-name


                            Example:
                            Device(config-subif)# xconnect 10.0.3.202 1234 encapsulation l2tpv3 pw-class l2tpv3
                             

                            Specifies the IP address of the peer provider edge (PE) device and the 32-bit virtual circuit identifier (VCI) that is shared between the PE device at each end of the control channel.

                            • The combination of the peer device ID and the VCI must be unique.
                            • pw-class pw-class-name—The pseudowire class configuration from which the data encapsulation type (L2TPv3) is taken. The pw-class parameter binds xconnect to a specific pseudowire class. The pseudowire class then serves as a template for all attachment circuits bound to it.
                             
                            Step 6 end


                            Example:
                            Device# end
                             

                            Exits subinterface configuration mode and returns to privileged EXEC mode.

                             

                            Configuring Frame Relay over L2TPv3

                            Figure 6. The Structure of the Frame Relay over L2TPv3



                            Configuring Frame Relay over L2TPv3 without LMI

                            The following sections show how to configure Frame Relay without LMI.

                            CE1 (DCE)

                            Perform the following steps to configure the Frame Relay over L2TPv3 without LMI on CE1:

                            SUMMARY STEPS

                              1.    enable

                              2.    configure terminal

                              3.    interface interface-id

                              4.    encapsulation frame-relay

                              5.    no keepalive

                              6.    frame-relay intf-type dce

                              7.    end

                              8.    enable

                              9.    configure terminal

                              10.    interface interface-id point-to-point

                              11.    ip address ip address subnet mask

                              12.    frame-relay interface-dlci interface-id

                              13.    end


                            DETAILED STEPS
                               Command or ActionPurpose
                              Step 1 enable


                              Example:
                              Router> enable
                               

                              Enables privileged EXEC mode.

                              Enter your password if prompted.

                               
                              Step 2 configure terminal


                              Example:
                              Router# configure terminal
                               

                              Enters global configuration mode.

                               
                              Step 3 interface interface-id


                              Example:
                              Router(config)# interface Serial2/1:0
                               

                              Specifies the interface, and enters interface configuration mode.

                               
                              Step 4 encapsulation frame-relay


                              Example:
                              Router(config-if)# encapsulation frame-relay
                               

                              Enables Frame Relay encapsulation.

                               
                              Step 5 no keepalive


                              Example:
                              Router(config-if)# no keepalive
                               

                              Disables keepalive packets.

                               
                              Step 6 frame-relay intf-type dce


                              Example:
                              Router(config-if)# frame-relay intf-type dce
                               

                              Configures a Frame Relay switch type as router.

                               
                              Step 7 end


                              Example:
                              Router(config-if)# end
                               

                              Ends the current configuration session.

                               
                              Step 8 enable


                              Example:
                              Router> enable
                               

                              Enables privileged EXEC mode.

                               
                              Step 9 configure terminal


                              Example:
                              Router# configure terminal
                               

                              Enters global configuration mode.

                               
                              Step 10interface interface-id point-to-point


                              Example:
                              Router(config-if)# interface Serial2/1:0.1 point-to-point
                               

                              Enters global configuration mode.

                               
                              Step 11 ip address ip address subnet mask


                              Example:
                              Router(config-if)# ip address 32.0.0.2 255.255.255.0
                               

                              Specifies the IP address and the subnet mask.

                               
                              Step 12frame-relay interface-dlci interface-id


                              Example:
                              Router(config-if)# frame-relay interface-dlci 50
                               

                              Assigns a data-link connection identifier (DLCI) to a specified Frame Relay subinterface on the router.

                               
                              Step 13 end


                              Example:
                              Router(config-if)# end
                               

                              Ends the current configuration session.

                               
                              PE1(DTE)

                              Perform the following steps to configure the Frame Relay over L2TPv3 without LMI on PE1:

                              SUMMARY STEPS

                                1.    enable

                                2.    configure terminal

                                3.    interface interface-id

                                4.    no ip address

                                5.    encapsulation frame-relay

                                6.    no keepalive

                                7.    pseudowire-class pw-class-name

                                8.    encapsulation l2tpv3

                                9.    ip local interface loopback loopback-id

                                10.    connect connection-name interface-id l2transport

                                11.    xconnect peer-ip-address vc-id encapsulation l2tpv3 pw-class l2tpv3


                              DETAILED STEPS
                                 Command or ActionPurpose
                                Step 1 enable


                                Example:
                                Router> enable
                                 

                                Enables privileged EXEC mode.

                                Enter your password if prompted.

                                 
                                Step 2 configure terminal


                                Example:
                                Router# configure terminal
                                 

                                Enters global configuration mode.

                                 
                                Step 3 interface interface-id


                                Example:
                                Router(config)# interface Serial0/1/0:0
                                 

                                Specifies the interface, and enters interface configuration mode.

                                 
                                Step 4 no ip address


                                Example:
                                Router(config-if)# no ip address
                                 

                                Removes all the IP addresses in the interface.

                                 
                                Step 5 encapsulation frame-relay


                                Example:
                                Router(config-if)# encapsulation frame-relay
                                 

                                Enables Frame Relay encapsulation.

                                 
                                Step 6 no keepalive


                                Example:
                                Router(config-if)# no keepalive
                                 

                                Disables keepalive packets.

                                 
                                Step 7 pseudowire-class pw-class-name


                                Example:
                                Router(config-if)# pseudowire-class l2tpv3
                                 

                                Specifies the name of a Layer 2 pseudowire class and enters pseudowire class configuration mode.

                                 
                                Step 8 encapsulation l2tpv3


                                Example:
                                Router(config-if)# encapsulation l2tpv3
                                 

                                Specifies that L2TPv3 is used as the data encapsulation method for tunneling IP traffic over the pseudowire.

                                 
                                Step 9 ip local interface loopback loopback-id


                                Example:
                                Router(config-if)# ip local interface loopback0
                                 

                                Specifies the local loopback interface.

                                 
                                Step 10 connect connection-name interface-id l2transport


                                Example:
                                Router(config-if)# connect fr_l2tpv3 Serial0/1/0:0 32 l2transport
                                 

                                Specifies that the PVC will not be a locally switched PVC, but will be tunneled over the backbone network.

                                 
                                Step 11 xconnect peer-ip-address vc-id encapsulation l2tpv3 pw-class l2tpv3


                                Example:
                                Router(config-if)# xconnect 3.3.3.3 32 encapsulation l2tpv3 pw-class l2tpv3
                                 

                                Binds an attachment circuit to a pseudowire, to configure an Any Transport over MPLS (AToM) static pseudowirwe. Specifies the pseudowire class for advanced configuration, and L2TPv3, as the tunneling method.

                                 

                                Configuring Frame Relay over L2TPv3 with LMI

                                The following sections show how to configure Frame Relay with LMI.

                                CE1(DCE)

                                Perform the following steps to configure the Frame Relay over L2TPv3 with LMI on CE1:
                                SUMMARY STEPS

                                  1.    enable

                                  2.    configure terminal

                                  3.    interface interface-id

                                  4.    encapsulation frame-relay

                                  5.    frame-relay intf-type dce

                                  6.    end


                                DETAILED STEPS
                                   Command or ActionPurpose
                                  Step 1 enable


                                  Example:
                                  Router> enable
                                   

                                  Enables privileged EXEC mode.

                                  Enter your password if prompted.

                                   
                                  Step 2 configure terminal


                                  Example:
                                  Router# configure terminal
                                   

                                  Enters global configuration mode.

                                   
                                  Step 3 interface interface-id


                                  Example:
                                  Router(config)# interface Serial2/1:0
                                   

                                  Specifies the interface, and enters interface configuration mode.

                                   
                                  Step 4 encapsulation frame-relay


                                  Example:
                                  Router(config-if)# encapsulation frame-relay
                                   

                                  Enables Frame Relay encapsulation.

                                   
                                  Step 5 frame-relay intf-type dce


                                  Example:
                                  Router(config-if)# frame-relay intf-type dce
                                   

                                  Configures a Frame Relay switch type as router.

                                   
                                  Step 6 end


                                  Example:
                                  Router(config-if)# end
                                   

                                  Ends the current configuration session.

                                   
                                  PE1(DTE)

                                  Perform the following steps to configure the Frame Relay over L2TPv3 with LMI on PE1:

                                  SUMMARY STEPS

                                    1.    enable

                                    2.    configure terminal

                                    3.    interface interface-id

                                    4.    encapsulation frame-relay

                                    5.    pseudowire-class pw-class-name

                                    6.    encapsulation l2tpv3

                                    7.    ip local interface loopback loopback-id

                                    8.    connect connection-name interface-id l2transport

                                    9.    xconnect peer-ip-address vc-id encapsulation l2tpv3 pw-class l2tpv3


                                  DETAILED STEPS
                                     Command or ActionPurpose
                                    Step 1 enable


                                    Example:
                                    Router> enable
                                     

                                    Enables privileged EXEC mode.

                                    Enter your password if prompted.

                                     
                                    Step 2 configure terminal


                                    Example:
                                    Router# configure terminal
                                     

                                    Enters global configuration mode.

                                     
                                    Step 3 interface interface-id


                                    Example:
                                    Router(config)# interface Serial0/1/0:0
                                     

                                    Specifies the interface, and enters interface configuration mode.

                                     
                                    Step 4 encapsulation frame-relay


                                    Example:
                                    Router(config-if)# encapsulation frame-relay
                                     

                                    Enables Frame Relay encapsulation.

                                     
                                    Step 5 pseudowire-class pw-class-name


                                    Example:
                                    Router(config-if)# pseudowire-class l2tpv3
                                     

                                    Specifies the name of a Layer 2 pseudowire class and enters pseudowire class configuration mode.

                                     
                                    Step 6 encapsulation l2tpv3


                                    Example:
                                    Router(config-if)# encapsulation l2tpv3
                                     

                                    Specifies that L2TPv3 is used as the data encapsulation method for tunneling IP traffic over the pseudowire.

                                     
                                    Step 7 ip local interface loopback loopback-id


                                    Example:
                                    Router(config-if)# ip local interface loopback0
                                     

                                    Specifies the local loopback interface.

                                     
                                    Step 8 connect connection-name interface-id l2transport


                                    Example:
                                    Router(config-if)# connect fr_l2tpv3 Serial0/1/0:0 32 l2transport
                                     

                                    Specifies that the PVC will not be a locally switched PVC, but will be tunneled over the backbone network.

                                     
                                    Step 9 xconnect peer-ip-address vc-id encapsulation l2tpv3 pw-class l2tpv3


                                    Example:
                                    Router(config-if)# xconnect 3.3.3.3 32 encapsulation l2tpv3 pw-class l2tpv3
                                     

                                    Binds an attachment circuit to a pseudowire, to configure an AToM static pseudowire. Specifies the pseudowire class for advanced configuration and specifies L2TPv3, as the tunneling method.

                                     

                                    Manually Clearing L2TPv3 Tunnels

                                    Perform this task to manually clear a specific L2TPv3 tunnel and all the sessions in that tunnel.

                                    SUMMARY STEPS

                                      1.    enable

                                      2.    clear l2tun {l2tp-class l2tp-class-name | tunnel id tunnel-id | local ip ip-address | remote ip ip-address | all}


                                    DETAILED STEPS
                                       Command or ActionPurpose
                                      Step 1 enable


                                      Example:
                                      Device> enable
                                       

                                      Enables privileged EXEC mode.

                                      • Enter your password if prompted.
                                       
                                      Step 2 clear l2tun {l2tp-class l2tp-class-name | tunnel id tunnel-id | local ip ip-address | remote ip ip-address | all}


                                      Example:
                                      Device# clear l2tun tunnel id 56789
                                       

                                      Clears the specified L2TPv3 tunnel. (This command is not available if there are no L2TPv3 tunnel sessions configured.)

                                      • l2tp-class l2tp-class-name—All L2TPv3 tunnels with the specified L2TP class name are torn down.
                                      • tunnel id tunnel-id—The L2TPv3 tunnel with the specified tunnel ID are torn down.
                                      • local ip ip-address—All L2TPv3 tunnels with the specified local IP address are torn down.
                                      • remote ip ip-address—All L2TPv3 tunnels with the specified remote IP address are torn down.
                                      • all—All L2TPv3 tunnels are torn down.
                                       

                                      Configuration Examples for Layer 2 Tunneling Protocol Version 3


                                      Note


                                      The IP addresses used in this document are not intended to be actual addresses. Any examples, command display output, and figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses in illustrative content is unintentional and coincidental.


                                      Example: Configuring a Static L2TPv3 Session for an Xconnect Ethernet Interface

                                      L2TPv3 is the only encapsulation method that supports a manually provisioned session setup. This example shows how to configure a static session configuration in which all control channel parameters are set up in advance. There is no control plane used and no negotiation phase to set up the control channel. The PE device starts sending tunneled traffic as soon as the Ethernet interface (int e0/0) comes up. The virtual circuit identifier, 123, is not used. The PE sends L2TP data packets with session ID 111 and cookie 12345. In turn, the PE expects to receive L2TP data packets with session ID 222 and cookie 54321.

                                      l2tp-class l2tp-defaults
                                       retransmit initial retries 30
                                       cookie-size 8
                                      pseudowire-class ether-pw
                                       encapsulation l2tpv3
                                       protocol none
                                       ip local interface Loopback0
                                      interface Ethernet 0/0
                                       xconnect 10.0.3.201 123 encapsulation l2tpv3 manual pw-class ether-pw
                                       l2tp id 222 111
                                       l2tp cookie local 4 54321
                                       l2tp cookie remote 4 12345
                                       l2tp hello l2tp-defaults

                                      Example: Configuring a Negotiated L2TPv3 Session for an Xconnect VLAN Subinterface

                                      The following is a sample configuration of a dynamic L2TPv3 session for a VLAN xconnect interface. In this example, only VLAN traffic with a VLAN ID of 5 is tunneled. In the other direction, the L2TPv3 session identified by a virtual circuit identifier of 123 receives forwarded frames whose VLAN ID fields are rewritten to contain the value 5. L2TPv3 is used as both the control plane protocol and the data encapsulation.

                                      l2tp-class class1
                                       authentication
                                       password secret
                                      pseudowire-class vlan-xconnect
                                       encapsulation l2tpv3
                                       protocol l2tpv3 class1
                                       ip local interface Loopback0
                                      interface Ethernet0/0.1
                                       encapsulation dot1q 5
                                       xconnect 10.0.3.201 123 pw-class vlan-xconnect

                                      Example: Configuring a Negotiated L2TPv3 Session for Local HDLC Switching

                                      The following is a sample configuration of a dynamic L2TPv3 session for local HDLC switching. In this example, note that it is necessary to configure two different IP addresses at the endpoints of the L2TPv3 pseudowire because the virtual circuit identifier must be unique for a given IP address.

                                      interface loopback 1
                                       ip address 10.0.0.1 255.255.255.255
                                      interface loopback 2
                                       ip address 10.0.0.2 255.255.255.255
                                      pseudowire-class loopback1
                                       encapsulation l2tpv3
                                       ip local interface loopback1
                                      pseudowire-class loopback2
                                       encapsulation l2tpv3
                                       ip local interface loopback2
                                      interface s0/0
                                       encapsulation hdlc
                                       xconnect 10.0.0.1 100 pw-class loopback2
                                      interface s0/1
                                       encapsulation hdlc
                                       xconnect 10.0.0.2 100 pw-class loopback1

                                      Example: Verifying an L2TPv3 Session

                                      To display information about current L2TPv3 sessions on a device, use the show l2tun session brief command.

                                      Device# show l2tun session brief
                                      L2TP Session Information Total tunnels 1 sessions 1
                                      LocID      TunID      Peer-address    State     Username, Intf/                 
                                                                            sess/cir  Vcid, Circuit                   
                                      2391726297 2382731778 6.6.6.6         est,UP    100, Gi0/2/0

                                      To display detailed information about current L2TPv3 sessions on a device, use the show l2tun session all command.

                                      Device# show l2tun session all
                                      L2TP Session Information Total tunnels 1 sessions 1
                                      Session id 2391726297 is up, logical session id 36272, tunnel id 2382731778
                                        Remote session id is 193836624, remote tunnel id 2280318174
                                        Locally initiated session
                                        Unique ID is 12
                                      Session Layer 2 circuit, type is Ethernet, name is GigabitEthernet0/2/0
                                        Session vcid is 100
                                        Circuit state is UP
                                          Local circuit state is UP
                                          Remote circuit state is UP
                                      Call serial number is 98300002
                                      Remote tunnel name is l2tp-asr-2
                                        Internet address is 6.6.6.6
                                      Local tunnel name is l2tp-asr-1
                                        Internet address is 3.3.3.3
                                      IP protocol 115
                                        Session is L2TP signaled
                                        Session state is established, time since change 00:05:25
                                          94 Packets sent, 58 received
                                          9690 Bytes sent, 5642 received
                                        Last clearing of counters never
                                        Counters, ignoring last clear:
                                          94 Packets sent, 58 received
                                          9690 Bytes sent, 5642 received
                                          Receive packets dropped:
                                            out-of-order:             0
                                            other:                    0
                                            total:                    0
                                      Send packets dropped:
                                            exceeded session MTU:     0
                                            other:                    0
                                            total:                    0
                                        DF bit off, ToS reflect disabled, ToS value 0, TTL value 255
                                        Sending UDP checksums are disabled
                                        Received UDP checksums are verified
                                        No session cookie information available
                                        FS cached header information:
                                          encap size = 24 bytes
                                          45000014 00000000 ff73a965 03030303
                                          06060606 0b8db650 
                                        Sequencing is off
                                        Conditional debugging is disabled
                                        SSM switch id is 4101, SSM segment id is 12294

                                      Example: Verifying an L2TP Control Channel

                                      The L2TP control channel is used to negotiate capabilities, monitor the health of the peer PE device, and set up various components of an L2TPv3 session.

                                      To display information about L2TP control channels to other L2TP-enabled devices for all L2TP sessions on the device, use the show l2tun tunnel command.
                                      Device# show l2tun tunnel
                                      L2TP Tunnel Information Total tunnels 1 sessions 1
                                      LocTunID   RemTunID   Remote Name   State  Remote Address  Sessn L2TP Class/
                                                                                                 Count VPDN Group 
                                      2382731778 2280318174 l2tp-asr-2    est    6.6.6.6         1     l2tp_default_cl
                                      To display detailed information about L2TP control channels to other L2TP-enabled devices for all L2TP sessions on the device, use the show l2tun tunnel all command.
                                      Device# show l2tun tunnel all 
                                      L2TP Tunnel Information Total tunnels 1 sessions 1
                                      Tunnel id 2382731778 is up, remote id is 2280318174, 1 active sessions
                                        Locally initiated tunnel
                                        Tunnel state is established, time since change 00:02:59
                                        Tunnel transport is IP  (115)
                                        Remote tunnel name is l2tp-asr-2
                                          Internet Address 6.6.6.6, port 0
                                        Local tunnel name is l2tp-asr-1
                                          Internet Address 3.3.3.3, port 0
                                        L2TP class for tunnel is l2tp_default_class
                                        Counters, taking last clear into account:
                                          54 packets sent, 35 received
                                          5676 bytes sent, 3442 received
                                        Last clearing of counters never
                                        Counters, ignoring last clear:
                                          54 packets sent, 35 received
                                          5676 bytes sent, 3442 received
                                      Control Ns 5, Nr 4
                                        Local RWS 1024 (default), Remote RWS 1024
                                        Control channel Congestion Control is disabled
                                        Tunnel PMTU checking disabled
                                        Retransmission time 1, max 1 seconds
                                        Unsent queuesize 0, max 0
                                        Resend queuesize 0, max 2
                                        Total resends 0, ZLB ACKs sent 2
                                        Total out-of-order dropped pkts 0 
                                        Total out-of-order reorder pkts 0 
                                        Total peer authentication failures 0
                                        Current no session pak queue check 0 of 5
                                        Retransmit time distribution: 0 0 0 0 0 0 0 0 0 
                                        Control message authentication is disabled

                                      Example: Configuring L2TPv3 Control Channel Authentication

                                      The following example shows how to configure CHAP-style authentication of the L2TPv3 control channel:
                                      l2tp-class class0
                                       authentication
                                       password cisco
                                      The following example shows how to configure control channel authentication using the L2TPv3 Control Message Hashing feature:
                                      l2tp-class class1
                                       digest secret cisco hash sha
                                       hidden
                                      The following example shows how to configure control channel integrity checking and how to disable validation of the message digest using the L2TPv3 Control Message Hashing feature:
                                      l2tp-class class2
                                       digest hash sha
                                       no digest check
                                      The following example shows how to disable the validation of the message digest using the L2TPv3 Control Message Hashing feature:
                                      l2tp-class class3
                                       no digest check

                                      Example: Configuring L2TPv3 Digest Secret Graceful Switchover

                                      The following example shows how to use the L2TPv3 Digest Secret Graceful Switchover feature to change the L2TP control channel authentication password for the L2TP class named class1. This example assumes that you already have an old password configured for the L2TP class named class1.

                                      Device(config)# l2tp-class class1
                                      Device(config-l2tp-class)# digest secret cisco2 hash sha
                                      !
                                      ! Verify that all peer PE devices have been updated to use the new password before
                                      ! removing the old password.
                                      !
                                      Device(config-l2tp-class)# no digest secret cisco hash sha

                                      Example: Verifying L2TPv3 Digest Secret Graceful Switchover

                                      The following show l2tun tunnel all command output shows information about the L2TPv3 Digest Secret Graceful Switchover feature:

                                      Device# show l2tun tunnel all
                                      ! The output below displays control channel password information for a tunnel which has
                                      ! been updated with the new control channel authentication password.
                                      !
                                      Tunnel id 12345 is up, remote id is 54321, 1 active sessions
                                      Control message authentication is on, 2 secrets configured
                                      Last message authenticated with first digest secret
                                      !
                                      ! The output below displays control channel password information for a tunnel which has
                                      ! only a single control channel authentication password configured.
                                      !
                                      Tunnel id 23456 is up, remote id is 65432, 1 active sessions
                                      !
                                      Control message authentication is on, 1 secrets configured
                                      Last message authenticated with first digest secret
                                      !
                                      ! The output below displays control channel password information for a tunnel which is
                                      ! communicating with a peer that has only the new control channel authentication password ! configured.
                                      !
                                      Tunnel id 56789 is up, remote id is 98765, 1 active sessions
                                      !
                                      Control message authentication is on, 2 secrets configured
                                      Last message authenticated with second digest secret

                                      Example: Configuring a Pseudowire Class for Fragmentation of IP Packets

                                      The following is a sample configuration of a pseudowire class that will allow IP traffic generated from the CE device to be fragmented before entering the pseudowire:

                                      pseudowire class class1
                                       encapsulation l2tpv3
                                       ip local interface Loopback0
                                       ip pmtu
                                       ip dfbit set

                                      Example: Configuring Protocol Demultiplexing for L2TPv3

                                      The following example shows how to configure the L2TPv3 Protocol Demultiplexing feature on IPv4 PE devices. The PE devices facing the IPv6 network do not require the IPv6 configuration.

                                      interface ethernet 0/1
                                       ip address 172.16.128.4
                                       xconnect 10.0.3.201 888 pw-class demux
                                        match protocol ipv6

                                      Example: Manually Clearing an L2TPv3 Tunnel

                                      The following example demonstrates how to manually clear a specific L2TPv3 tunnel using the tunnel ID:

                                      clear l2tun tunnel 65432

                                      Example: Configuring an L2TPv3 Custom Ethertype for Dot1q and QinQ Encapsulations

                                      The following example shows how to configure an Ethertype other than 0x8100 on Gigabit Ethernet interfaces with QinQ or dot1Q encapsulations. In this example, the Ethertype field is set to 0x9100 on Gigabit Ethernet interface 1/0/0.

                                      Device> enable
                                      Device# configure terminal
                                      Device(config)# interface gigabitethernet 1/0/0
                                      Device(config-if)# dot1q tunneling ethertype 0x9100

                                      Example: Configuring an L2TPv3 HDLC Like-to-Like Layer 2 Transport

                                      Example: Configuring an L2TPv3 HDLC Like-to-Like Layer 2 Transport on Dynamic Mode

                                      The following example shows how to configure xconnect on a serial interface with HDLC encapsulation on a dynamic mode. The dynamic mode uses L2TPv3 signaling in control channel to set up the L2TPv3 tunnel.

                                      pseudowire-class 774
                                       encapsulation l2tpv3
                                       protocol l2tpv3
                                       ip local interface GigabitEthernet0/0/1.774
                                      !
                                      interface Serial0/2/0:0
                                       no ip address
                                       xconnect 4.4.4.4 200 pw-class 774

                                      Example: Configuring an L2TPv3 HDLC Like-to-Like Layer 2 Transport on Static Mode

                                      The following example shows how to configure xconnect on a serial interface with HDLC encapsulation on a static mode. The static mode is used to disable signaling in the L2TPv3 control channel. Since signaling is disabled, you must specify the manual option in xconnect and configure L2TP-specific parameters to complete the L2TPv3 control channel configuration.

                                      pseudowire-class pe1-ether-pw
                                       encapsulation l2tpv3
                                       protocol none
                                       ip local interface Loopback1
                                      !
                                      interface Serial0/2/0:0
                                       no ip address
                                       xconnect 2.2.2.2 50 encapsulation l2tpv3 manual pw-class pe1-ether-pw
                                        l2tp id 111 111
                                        l2tp cookie local 4 54321
                                        l2tp cookie remote 4 12345

                                      Example: Configuring GEC over L2TPv3

                                      The following is a sample configuration of Gigabit EtherChannel (GEC) over Layer 2 Tunneling Protocol Version 3 (L2TPv3):

                                      Device> enable
                                      Device# configure terminal
                                      Device(config)# interface Loopback0
                                      Device(config-if)# ip address 10.1.0.1 255.255.255.255
                                      Device(config-if)# exit
                                      Device(config)# pseudowire-class l2tpv3
                                      Device(config-pw)# encapsulation l2tpv3
                                      Device(config-pw)# ip local interface loopback0
                                      Device(config-if)# exit
                                      Device(config)# interface port-channel 1
                                      Device(config-if)# xconnect 1.1.1.1 1234 encapsulation l2tpv3 pw-class l2tpv3 
                                      Device(config-if)# exit
                                      Device(config)# interface g0/0/0
                                      Device(config-if)# channel-group 1
                                      Device(config-if)# end
                                      
                                      

                                      Example: Configuring GEC with Dot1q over L2TPv3

                                      The following is a sample configuration of a Gigabit EtherChannel (GEC) with dot1q over Layer 2 Tunneling Protocol Version 3 (L2TPv3):

                                      Device> enable
                                      Device# configure terminal
                                      Device(config)# interface port-channel 1
                                      Device(config-if)# interface port-channel 1.1
                                      Device(config-subif)# encapsulation dot1q 100
                                      Device(config-subif)# xconnect 10.0.0.2 1234 encapsulation l2tpv3 pw-class l2tpv3  
                                      Device(config-subif)# end  
                                      

                                      Example: Configuring GEC with QinQ over L2TPv3

                                      The following is a sample configuration of a Gigabit EtherChannel (GEC) with queue-in-queue (QinQ) over Layer 2 Tunneling Protocol Version 3 (L2TPv3):

                                      Device> enable
                                      Device# configure terminal
                                      Device(config)# interface port-channel 1
                                      Device(config-if)# interface port-channel 1.1
                                      Device(config-subif)# encapsulation dot1q 100 second-dot1q 200
                                      Device(config-subif)# xconnect 10.0.0.3 1234 encapsulation l2tpv3 pw-class l2tpv3  
                                      Device(config-subif)# end
                                        
                                      

                                      Example: Configuring Frame Relay over L2TPv3

                                      Frame Relay over L2TPv3 without LMI

                                      CE1(DCE):

                                      interface Serial2/1:0
                                       no ip address
                                       encapsulation frame-relay
                                      no keepalive
                                       frame-relay intf-type dce
                                      end
                                      interface Serial2/1:0.1 point-to-point
                                       ip address 32.0.0.2 255.255.255.0
                                       frame-relay interface-dlci 32
                                      end
                                      

                                      PE1(DTE):

                                      interface Serial0/1/0:0
                                       no ip address
                                       encapsulation frame-relay
                                      no keepalive
                                      
                                      pseudowire-class l2tpv3
                                       encapsulation l2tpv3
                                       ip local interface Loopback0
                                      
                                      connect fr_l2tpv3 Serial0/1/0:0 32 l2transport
                                       xconnect 3.3.3.3 32 encapsulation l2tpv3 pw-class l2tpv3
                                      

                                      Frame Relay over L2TPv3 with LMI

                                      CE1(DCE):

                                      interface Serial2/1:0
                                       no ip address
                                       encapsulation frame-relay
                                       frame-relay intf-type dce
                                      end
                                      interface Serial2/1:0.1 point-to-point
                                       ip address 32.0.0.2 255.255.255.0
                                       frame-relay interface-dlci 32
                                      end
                                      

                                      PE1(DTE):

                                      interface Serial0/1/0:0
                                       no ip address
                                       encapsulation frame-relay
                                      
                                      pseudowire-class l2tpv3
                                       encapsulation l2tpv3
                                       ip local interface Loopback0
                                      
                                      connect fr_l2tpv3 Serial0/1/0:0 32 l2transport
                                       xconnect 3.3.3.3 32 encapsulation l2tpv3 pw-class l2tpv3
                                      

                                      Frame Relay over L2TPv3 QoS Marking

                                      class-map match-all fr
                                       match fr-dlci  50
                                      policy-map dlci50
                                       class fr
                                        set ip precedence tunnel 3
                                      interface Serial0/1/0:0
                                      no ip address
                                       encapsulation frame-relay
                                       no keepalive
                                      service-policy input dlci50
                                      end
                                      
                                      pseudowire-class l2tpv3
                                       encapsulation l2tpv3
                                       ip local interface Loopback0
                                      
                                      connect fr_l2tpv3 Serial0/1/0:0 50 l2transport
                                       xconnect 3.3.3.3 55 encapsulation l2tpv3 pw-class l2tpv3
                                      

                                      Additional References

                                      Related Documents

                                      Related Topic

                                      Document Title

                                      Cisco IOS commands

                                      Master Commands List, All Releases

                                      WAN commands: complete command syntax, command mode, defaults, usage guidelines and examples

                                      Wide-Area Networking Command Reference

                                      Layer 2 Tunnel Protocol Version 3

                                      Layer 2 Tunneling Protocol Version 3

                                      Any Transport over MPLS

                                      Any Transport over MPLS

                                      Cisco 12000 series routers hardware support

                                      Cross-Platform Release Notes for Cisco IOS Release 12.0S

                                      Cisco 7600 series routers hardware support

                                      Cross-Platform Release Notes for Cisco IOS Release 12.2SR

                                      Cisco 3270 series routers hardware support

                                      Release Notes for Cisco IOS Software Release 12.2SE

                                      Standards and RFCs

                                      Standard/RFC

                                      Title

                                      draft-ietf-l2tpext-l2tp-base-03.txt

                                      Layer Two Tunneling Protocol (Version 3) 'L2TPv3'

                                      draft-martini-l2circuit-trans-mpls-09.txt

                                      Transport of Layer 2 Frames Over MPLS

                                      draft-ietf-pwe3-frame-relay-03.txt.

                                      Encapsulation Methods for Transport of Frame Relay over MPLS Networks

                                      draft-martini-l2circuit-encap-mpls-04.txt.

                                      Encapsulation Methods for Transport of Layer 2 Frames Over IP and MPLS Networks

                                      draft-ietf-pwe3-ethernet-encap-08.txt.

                                      Encapsulation Methods for Transport of Ethernet over MPLS Networks

                                      draft-ietf-pwe3-hdlc-ppp-encap-mpls-03.txt.

                                      Encapsulation Methods for Transport of PPP/HDLC over MPLS Networks

                                      draft-ietf-ppvpn-l2vpn-00.txt.

                                      An Architecture for L2VPNs

                                      MIBs

                                      MIBs

                                      MIBs Link

                                      No new or modified MIBs are supported by this feature, and support for existing MIBs has not been modified by this feature.

                                      To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:

                                      http:/​/​www.cisco.com/​go/​mibs

                                      Technical Assistance

                                      Description

                                      Link

                                      The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password.

                                      http:/​/​www.cisco.com/​cisco/​web/​support/​index.html

                                      Feature Information for Layer 2 Tunneling Protocol Version 3

                                      The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.

                                      Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/​go/​cfn. An account on Cisco.com is not required.

                                      Table 3 Feature Information for Layer 2 Tunneling Protocol Version 3

                                      Feature Name

                                      Releases

                                      Feature Information

                                      Layer 2 Tunneling Protocol Version 3

                                      XE 2.6

                                      XE 2.6.2

                                      XE 3.3S

                                      XE 3.11S

                                      The Layer 2 Tunneling Protocol Version 3 (L2TPv3) feature expands Cisco's support of Layer 2 VPNs.

                                      In Cisco IOS XE Release 2.6, the following features were added:

                                      • Ethernet over L2TPv3
                                      • Layer 2 VPN (L2VPN): Syslog, SNMP Trap, and show Command Enhancements for AToM and L2TPv3
                                      • L2TPv3 Control Message Hashing
                                      • L2TPv3 Control Message Rate Limiting
                                      • L2TPv3 Digest Secret Graceful Switchover
                                      • L2TPv3 Protocol Demultiplexing
                                      • L2TPv3 Custom Ethertype for Dot1q and QinQ Encapsulations

                                      In Cisco IOS XE Release 2.6.2, support was added for the ip pmtu command.

                                      In Cisco IOS XE Release 3.3S, support for HDLC over L2TPv3 was added.

                                      The following commands were introduced or modified: clear l2tun, debug vpdn, ip pmtu, l2tp cookie local, l2tp cookie remote l2tp hello, l2tp id, and xconnect.

                                      Glossary

                                      AV pairs—Attribute-value pairs.

                                      CEF—Cisco Express Forwarding. The Layer 3 IP switching technology that optimizes network performance and scalability for networks with large and dynamic traffic patterns.

                                      data-link control layer—Layer 2 in the SNA architectural model. Responsible for the transmission of data over a particular physical link. Corresponds approximately to the data link layer of the OSI model.

                                      DCE—Data circuit-terminating equipment (ITU-T expansion). Devices and connections of a communications network that comprise the network end of the user-to-network interface.

                                      DF bit—Don’t Fragment bit. The bit in the IP header that can be set to indicate that the packet should not be fragmented.

                                      DTE—Data terminal equipment. The device at the user end of a user-network interface that serves as a data source, destination, or both.

                                      HDLC—High-Level Data Link Control. A generic link-level communications protocol developed by the ISO. HDLC manages synchronous, code-transparent, serial information transfer over a link connection.

                                      ICMP—Internet Control Message Protocol. A network protocol that handles network errors and error messages.

                                      IDB— Interface descriptor block.

                                      IS-IS—Intermediate System-to-Intermediate System. The OSI link-state hierarchical routing protocol based on DECnet Phase V routing, whereby ISs (devices) exchange routing information based on a single metric to determine network topology.

                                      L2TP—An extension to PPP that merges features of two tunneling protocols: Layer 2 Forwarding (L2F) from Cisco Systems and Point-to-Point Tunneling Protocol (PPTP) from Microsoft. L2TP is an IETF standard endorsed by Cisco Systems and other networking industry leaders.

                                      L2TPv3—The draft version of L2TP that enhances functionality in RFC 2661 (L2TP).

                                      LMI—Local Management Interface.

                                      MPLS—Multiprotocol Label Switching. A switching method that forwards IP traffic using a label. This label instructs the devices in the network where to forward packets based on preestablished IP routing information.

                                      MQC—Modular quality of service CLI.

                                      MTU—Maximum Transmission Unit. The maximum packet size, in bytes, that a particular interface can handle.

                                      PMTU—Path MTU.

                                      PVC—Permanent virtual circuit. A virtual circuit that is permanently established. A Frame Relay logical link, whose endpoints and class of service are defined by network management. Analogous to an X.25 permanent virtual circuit, a PVC consists of the originating Frame Relay network element address, originating data-link control identifier, terminating Frame Relay network element address, and termination data-link control identifier. Originating refers to the access interface from which the PVC is initiated. Terminating refers to the access interface at which the PVC stops. Many data network customers require a PVC between two points. PVCs save the bandwidth associated with circuit establishment and tear down in situations where certain virtual circuits must exist all the time. Data terminating equipment with a need for continuous communication uses PVCs.

                                      PW—Pseudowire.

                                      SNMP—Simple Network Management Protocol. The network management protocol used almost exclusively in TCP/IP networks. SNMP provides a means to monitor and control network devices and manage configurations, statistics collection, performance, and security.

                                      tunneling—Architecture that is designed to provide the services necessary to implement any standard point-to-point encapsulation scheme.

                                      UNI—User-Network Interface.

                                      VPDN—Virtual private dialup network. A network that allows separate and autonomous protocol domains to share common access infrastructure, including modems, access servers, and ISDN devices. A VPDN enables users to configure secure networks that take advantage of ISPs that tunnel remote access traffic through the ISP cloud.