Table of Contents

Configuring Tag Switching and MPLS

This chapter describes tag switching, a high-performance packet-forwarding technology that assigns tags to mulitprotocol frames for transport across packet- or cell-based networks.

Note   This chapter provides advanced configuration instructions for the Catalyst 8540 MSR, Catalyst 8510 MSR, and LightStream 1010 ATM switch routers. For an overview of tag switching, refer to the Guide to ATM Technology. For complete descriptions of the commands mentioned in this chapter, refer to the ATM Switch Router Command Reference publication.

This chapter includes the following sections:

Tag Switching Overview

In conventional Layer 3 forwarding, as a packet traverses the network, each router extracts forwarding information from the Layer 3 header. Header analysis is repeated at each router (hop) through which the packet passes.

In a tag switching network, the Layer 3 header is analyzed just once. It is then mapped into a short fixed-length tag. At each hop, the forwarding decision is made by looking only at the value of the tag. There is no need to reanalyze the Layer 3 header. Because the tag is a fixed-length, unstructured value, lookup is fast and simple.

For an overview of how tag switching works and its benefits, refer to the Guide to ATM Technology.

Hardware and Software Requirements and Restrictions (Catalyst 8540 MSR)

The Catalyst 8540 MSR hardware requirements for tag switching include the following:

Tag switching has the following software restrictions:

Hardware and Software Requirements and Restrictions (Catalyst 8510 MSR and LightStream 1010)

The Catalyst 8510 MSR and LightStream 1010 ATM switch router hardware requirements for tag switching include the following:

Tag switching has the following software restrictions:

Configuring Tag Switching

This section describes how to configure tag switching on ATM switch routers, and includes the following procedures:

Configuring a Loopback Interface

You should configure a loopback interface on every ATM switch router configured for tag switching. The loopback interface, a virtual interface, is always active. The IP address of the loopback interface is used as the Tag Distribution Protocol (TDP) identifier for the ATM switch router. If a loopback interface does not exist, the TDP identifier is the highest IP address configured on the ATM switch router. If that IP address is administratively shut down, all TDP sessions through the ATM switch router restart. Therefore, we recommend that you configure a loopback interface.

To configure the loopback interface, perform the following steps, beginning in global configuration mode:

Example

In the following example, loopback interface 0 is created with an IP address of 1.0.1.11 and a subnet mask of 255.255.255.255:

Displaying Loopback Interface Configuration

The following example shows the loopback 0 configuration using the show interfaces privileged EXEC command:

Enabling Tag Switching on the ATM Interface

Note   Configure all parallel interfaces between ATM switch routers for either IP unnumbered or with a specific IP address. Unnumbering some parallel interfaces and assigning specific IP addresses to others might cause TDP sessions to restart on some parallel interfaces when another parallel interface is shut down. Therefore, we highly recommend that you unnumber all parallel interfaces to loopback.

To enable tag switching on the ATM interface, perform the following steps, beginning in global configuration mode:

Examples

In the following example, ATM interface 1/0/1 is configured for IP unnumbered to loopback interface 0:

In the following example, ATM interface 0/0/3 is configured with a specific IP address and subnet mask (1.3.11.3 255.255.0.0):

Displaying the ATM Interface Configuration

To display the ATM interface configuration, use the following EXEC command:

The following example shows that tag switching is configured on ATM interfaces 0/0/3 and 1/0/1:

Configuring OSPF

Enable OSPF on the ATM switch router so that it can create routing tables, which identify routes through the network. Then add the addresses and associated routing areas to the OSPF process so that it can propagate the addresses to other ATM switch routers:

Note   Since the 12.0(1a)W5(5b) release of the system software, addressing the interface on the route processor (CPU) has changed. The ATM interface is now called atm0, and the Ethernet interface is now called ethernet0. Old formats (atm 2/0/0 and ethernet 2/0/0) are still supported.

Example

The following is an example of OSPF enabled and assigned process number 10000. All addresses are in area 0:

Note   An IP address of 1.1.1.1 with a subnet mask of 255.255.255.0 is entered as an IP network prefix of 1.1.1.0 with a subnet mask of 0.0.0.255. Likewise, an IP address of 1.2.1.1 with a subnet mask of 255.255.255.0 is entered as an IP network prefix of 1.2.1.0 with a subnet mask of 0.0.0.255.

Displaying the OSPF Configuration

To display the OSPF configuration, use the following privileged EXEC command:

The following example shows the OSPF configuration using the show ip ospf privileged EXEC command:

Configuring a VPI Range (Optional)

Although not necessary for most configurations, you might need to change the default tag virtual path identifier (VPI) range on the switch if:

To change the default tag VPI range, perform the following steps, beginning in global configuration mode:

Examples

The following example shows how to select a VPI range from 5 to 6 (a range of two), an acceptable range if the TDP neighbor is a router:

The following example shows how to select a VPI range from 5 to 7 (a range of three), an acceptable range if the TDP neighbor is a switch:

Note   Although the example shows a VPI range of three, you are not limited to a range of three if the TDP neighbor is a switch. The maximum VPI range is 0 to 255 if the TDP neighbor is a switch.

Displaying the Tag Switching VPI Range

To display the tag switching VPI range, use the following EXEC command:

Example

The following example shows the tag switching VPI range on ATM interface 1/0/1:

Configuring TDP Control Channels (Optional)

Although not necessary for most configurations, you can change the default Tag Distribution Protocol (TDP) control channel VPI and virtual channel identifier (VCI) if you want to use a nondefault value. The default TDP control channel is on VPI 0 and VCI 32. TDP control channels exchange TDP HELLOs and Protocol Information Elements (PIEs) to establish two-way TDP sessions. TVCs are created by the exchange of PIEs through TDP control channels.

To change the TDP control channel, perform the following steps, beginning in global configuration mode:

Figure 15-1 shows an example TDP control channel configuration between a source switch and destination switch on ATM interface 0/0/1. Note that the VPI and VCI values match on the source switch and destination switch.

Examples

In the following example, a TDP control channel is configured on the source switch:

In the following example, a TDP control channel is configured on the destination switch:

If you are having trouble establishing a TDP session, verify that the VPI and VCI values match on the TDP control channels of the source switch and destination switch.

Displaying the TDP Control Channels

To display the TDP control channel configuration, use the following EXEC command:

The following example shows the TDP control channel configuration on interface ATM 0/0/3:

Configuring Tag Switching on VP Tunnels

If you want to configure tag switching on virtual path (VP) tunnels, perform the following steps, beginning in global configuration mode:

Note   This procedure is optional.

Because a VP tunnel runs between switches, you must also configure a VP tunnel on the connecting ATM interface on the destination switch. The examples that follow show how to configure VP tunnels between switches.

Note   The intermediate switch configuration follows in the next section, "Connecting the VP Tunnels."

Figure 15-2 shows an example VP tunnel between a source switch and destination switch.

Examples

In the following example, ATM interface 0/1/1 on the source switch has no IP address and PVP 51 is configured for IP unnumbered to loopback interface 0:

In the following example, ATM interface 0/1/3 on the destination switch has no IP address and PVP 101 is configured for IP unnumbered to loopback interface 0:

To connect the source and destination switch VP tunnels, proceed to the next section, "Connecting the VP Tunnels."

Displaying the VP Tunnel Configuration

To display the VP tunnel configuration, use the following EXEC command:

The following example shows PVP 51 configured on ATM interface 0/1/1:

Connecting the VP Tunnels

To complete the VP tunnel, you must configure the ATM ports on the intermediate switch to designate where to send packets coming from the source switch and going to the destination switch.

To connect the permanent virtual path (PVP), perform the following steps, beginning in interface configuration mode:

Figure 15-3 shows an example configuration on an intermediate switch.

Example

In the following example, PVP 51 on ATM interface 0/1/1 is connected to PVP 101 on ATM interface 0/1/3:

Displaying the VP Tunnel Configuration

The following example shows PVP 51 on ATM interface 0/1/1 connected to PVP 101 on ATM interface 0/1/3:

Configuring VC Merge

VC merge allows the switch to aggregate multiple incoming flows with the same destination address into a single outgoing flow. Where VC merge occurs, several incoming tags are mapped to one single outgoing tag. Cells from different VCIs going to the same destination are transmitted to the same outgoing VC using multipoint-to-point connections. This sharing of tags reduces the total number of virtual circuits required for tag switching. Without VC merge, each source-destination prefix pair consumes one tag VC on each interface along the path. VC merge reduces the tag space shortage by sharing tags for different flows with the same destination.

Note   VC merge support requires FC-PFQ on the route processor. If you do not have FC-PFQ, and you try to enable VC merge, the TVCs remain point-to-point. (Catalyst 8510 MSR and LightStream 1010)

VC merge is enabled by default. To disable VC merge, enter the following command in global configuration mode:

Displaying the VC Merge Configuration

To display the VC merge configuration, use the following EXEC command:

The following example shows that VC merge configuration is enabled on ATM interface 0/1/0:

Configuring Tag Switching CoS

Quality of service (QoS) allows ATM to meet the transmission quality and service availability of many different types of data. The need for delay-sensitive data, such as voice, can be given a higher priority than data that is not delay-sensitive, such as e-mail. The following service categories were created for ATM Forum VCs to meet the transmission needs of various types of data: VBR-RT, VBR-NRT, ABR, and UBR. See "Configuring Resource Management," for more information about the standard ATM Forum implementation of QoS. This section describes tag switching class of service (CoS).

Up to eight QoS classes (0 to 7) can be allocated to each physical interface port. Each port has an independent logical rate scheduler (RS) and a weighted round-robin (WRR) scheduler. The RS guarantees minimum bandwidth and has first priority on supplying an eligible cell for transmission. Second priority is given to the service classes, which have been assigned relative weights that are based on the ratio of the total leftover bandwidth. The service class relative weights are configurable so you can change the priority of the default values. The VCs within a service class also have relative weights. The service classes and VCs within a service class are scheduled by their relative weights.

With tag switching CoS, tag switching can dynamically set up to four tag virtual channels (TVCs) with different service categories between a source and destination. TVCs do not share the same QoS classes reserved for ATM Forum VCs (VBR-RT, VBR-NRT, ABR, and UBR). The following four new service classes were created for TVCs: TBR_1 (WRR_1), TBR_2 (WRR_2), TBR_3 (WRR_3), and TBR_4 (WRR_4). These new service classes are called Tag Bit Rate (TBR) classes. TVCs and ATM Forum VCs can only coexist on the same physical interface, but they operate in ships in the night (SIN) mode and are unaware of each other.

TBR classes support only best-effort VCs (similar to the ATM Forum service category UBR); therefore, there is no bandwidth guarantee from the RS, which is not used for TVCs. All of the TVCs fall into one of the four TBR classes, each carrying a different default relative weight. The default values of the relative weights for the four TBR classes are configurable, so you can change the priority of the default values.

Table 15-1and Table 15-2 list the TBR classes and ATM Forum class mappings into the service classes for physical ports.

When tag switching is enabled on a hierarchical VP tunnel, the tunnel can only be used for tag switching. Because hierarchical VP tunnels support only four service classes, both TVCs and ATM Forum VCs map to the same service classes. Therefore, both ATM Forum VCs and TVCs cannot coexist in a hierarchical VP tunnel. The relative weights assigned to the service classes depend on which is active (either tag switching or ATM Forum). The class weights change whenever a hierarchical VP tunnel is toggled between ATM Forum and tag switching. By default, a hierarchical VP tunnel comes up as an ATM Forum port.

Table 15-3 and Table 15-4 list the TBR classes and ATM Forum service category mappings for hierarchical VP tunnels.

Configuring the Service Class and Relative Weight

Each service class is assigned a relative weight. These weights are configurable and range from 1 to 15.

To configure the service class and relative weight on a specific interface, perform the following steps, beginning in global configuration mode:

Example

In the following example, ATM interface 0/0/3 is configured with service class 1 and a WRR weight of 3:

Displaying the TVC Configuration

To display the TVC configuration, perform the following task in EXEC mode:

The following example shows the service category of the TVC:

Threshold Group for TBR Classes

A threshold group utilizes the memory efficiently among VCs of a particular traffic type. Each threshold group is programmed with a dynamic memory allocation profile that maps into the needs of the connections of a particular service class. There are 16 threshold groups (0 to 15) available on the ATM switch router. Each threshold group has a set of eight regions, and each region has a set of thresholds. When these thresholds are exceeded, cells are dropped to maintain the integrity of the shared memory resource.

Each ATM Forum service category is mapped into a distinct threshold group. All the connections in a particular service category map into one threshold group. Similarly, all the Tag Bit Rate (TBR) classes have best effort traffic and the service differentiation comes mainly by giving different weights. Each of the TBR classes map into four different threshold groups whose parameters are the same as the unspecified bit rate (UBR) threshold group.

Table 15-5 shows the threshold group parameters mapped to the connections in all of the TBR classes for the Catalyst 8540 MSR.

Table 15-6 shows the threshold group parameters mapped to the connections in all of the TBR classes for the Catalyst 8510 MSR and LightStream 1010 ATM switch routers.

Each threshold group is divided into eight regions. Each region has a set of thresholds that are calculated from the corresponding threshold group parameters given in Table 15-5. The threshold group might be in any one of the regions depending on the fill level (cell occupancy) of that group. And that region is used to derive the set of thresholds which apply to all the connections in that group.

Table 15-7 gives the eight thresholds for threshold groups 6, 7, 8, and 9.

For more information about threshold groups and configuration parameters, see "Configuring Resource Management," and the Guide to ATM Technology.

CTT Row

A row in the connection traffic table (CTT) is created for each unique combination of traffic parameters. When a TVC is set up in response to a request by tag switching, a CTT row is obtained from the resource manager by passing the traffic parameters that include the service category (TBR_x [WRR_x], where x is 1, 2, 3, or 4). If a match is found for the same set of traffic parameters, the row index is returned; otherwise a new table is created and the row index of that CTT row is returned. Since all data TVCs use the same traffic parameters, the same CTT row can be used for all TVCs of a particular service category once it is created.

Note   There are no user configurable parameters for the CTT with TVCs.

RM CAC Support

Connection admission control (CAC) is not supported for tag virtual channels (TVCs). All TVCs are best effort connections; therefore, no bandwidth is guaranteed by the RS. Only the WRR scheduler is used. So, all of the traffic parameters (PCR, MCR, MBS, CDVT, and SCR) are unspecified. There is no best effort limit like there is with ATM Forum UBR and ABR connections. CAC is bypassed for TVCs.

Tag Switching Configuration Example

Figure 15-4 shows an example tag switching network.

Router 5-1 Configuration

The configuration of router R5-1, interface e0/1, follows:

Router 5-2 Configuration

The configuration between router R5-1, interface e0/1, and R5-2, interface e0/1, follows:

The configuration between router R5-2, interface e0/2, and R5-3, interface e0/2, follows:

The configuration of router R5-2, interface a2/0.1, follows:

Router 5-3 Configuration

The configuration of router R5-3, interface e0/2, follows:

The configuration of router R5-3, interface e0/5 follows:

The configuration of router R5-3, interface atm 2/0.1, follows:

ATM Switch Router A5-4 Configuration

The configuration of ATM switch router A5-4, interfaces atm 0/1/1 and atm 0/0/3, follows:

Router 5-5 Configuration

The configuration of router R5-5, interface e0/2, follows:

ATM Switch Router A6-4 Configuration

The configuration of ATM switch router A6-4, interface atm 0/1/1, follows:

The configuration of ATM switch router A6-4, interface atm 0/0/3, follows:

MPLS Overview

MPLS Label Distribution Protocol (LDP), as standardized by the Internet Engineering Task Force (IETF) and as enabled by Cisco IOS software, allows the construction of highly scalable and flexible IP Virtual Private Networks (VPNs) that support multiple levels of services. MPLS offers the following benefits:

This section describes the Multiprotocol Label Switching (MPLS) distribution protocol. MPLS combines the performance and capabilities of Layer 2 (data link layer) switching with the proven scalability of Layer 3 (network layer) routing. This chapter includes the following sections:

Obtaining Additional MPLS Documentation

This chapter contains early field test MPLS configuration information for label edge routing (LER) and VPN networks on Fast Ethernet interfaces. For additional MPLS configuration documentation, refer to the sources in Table 15-8.

Hardware and Software Restrictions

The following restrictions or limitations apply to MPLS on the Catalyst 8540, Catalyst 8510 and LightStream 1010:

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Note    Fast Ethernet and ATM interfaces must be linked to an Enhanced ATM router module interface by using the mpls-forwarding command to provide MPLS support.

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Note    There is one master port per Ethernet processor interface (which controls four Fast Ethernet interfaces). For example, on an Ethernet processor interface controlling Fast Ethernet interfaces 2/0/0 through 2/0/3, Fast Ethernet interface 2/0/3 is the master port.

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MPLS/Tag Switching Terminology

Table 15-9 provides a conversion from the tag switching designations to the equivalent MPLS designations.

From an historical and functional standpoint, Label Distribution Protocol (LDP) is a superset of the pre-standard Cisco Tag Distribution Protocol (TDP), which also supports MPLS forwarding along normally routed paths. For those features that LDP and TDP share in common, the pattern of protocol exchanges between network routing platforms is identical. The differences between LDP and TDP for those features supported by both protocols are largely embedded in their respective implementation details. For more information on MPLS/tag switching terminology, refer to the Cisco IOS Switching Services Configuration Guide, Release 12.1.

How MPLS Works

In conventional Layer 3 forwarding, as a packet traverses the network, each router extracts all the information relevant to forwarding the packet from the Layer 3 header. This information is then used as an index for a routing table lookup to determine the packet's next hop.

In the most common case, the only relevant field in the header is the destination address field, but in some cases other header fields may also be relevant. As a result, the header analysis must be done independently at each router through which the packet passes, and a complicated lookup must also be done at each router.

In MPLS, the analysis of the Layer 3 header is done just once, when the packet enters the network at the ingress LSR (label switch router). This LSR reads the Layer 3 header and inserts a small fixed-format label in front of each data packet. For ATM MPLS connections, the label used is the VPI/VCI of the virtual circuit.The Layer 3 header is then mapped into a fixed length, unstructured value called a label.

Many different headers can map to the same label, as long as those headers always result in the same choice of next hop. In effect, a label represents a forwarding equivalence class—that is, a set of packets, which, however different they may be, are indistinguishable to the forwarding function.

The initial choice of label need not be based exclusively on the contents of the Layer 3 header; it can also be based on policy. This allows forwarding decisions at subsequent hops to be based on policy as well.

Once a label is chosen, a short label header is put at the front of the Layer 3 packet, so that the label value can be carried across the network with the packet. At each subsequent hop, the forwarding decision can be made simply by looking up the label. There is no need to re-analyze the header. Since the label is a fixed length an unstructured value, looking it up is fast and simple.

A label represents a forwarding equivalence class, but it does not represent a particular path through the network. In general, the path through the network continues to be chosen by the existing Layer 3 routing algorithms such as OSPF, Enhanced IGRP, and BGP. That is, at each hop when a label is looked up, the next hop chosen is determined by the dynamic routing algorithm.

The 32-bit MPLS label is located after the Layer 2 header and before the IP header. The MPLS label contains the following fields:

The MPLS label is also called a "Shim" header.

Distribution of Label Bindings

Each label switch router (LSR) in the network makes an independent, local decision as to which label value to use to represent an FEC. This association is known as label binding. Each LSR informs its neighbors of the label bindings it has made. This awareness of label bindings by neighboring routers and switches facilitates the following protocols:

MPLS LDP provides a standard methodology for hop-by-hop, or dynamic label, distribution in an MPLS network by assigning labels to routes that have been chosen by the underlying Interior Gateway Protocol (IGP) routing protocols. The resulting labeled paths, called label switch paths or LSPs, forward label traffic across an MPLS backbone to particular destinations. These capabilities enable service providers to implement Cisco MPLS-based IP VPNs and IP+ATM services across multi-vendor MPLS networks.

LDP allows label switch routers (LSRs) to request, distribute, and release label prefix binding information to peer routers in a network. LDP enables LSRs to discover potential peers and to establish LDP sessions with those peers to exchange label binding information.

An LDP label binding is an association between a destination prefix and a label. The label used in a label binding is allocated from a set of possible labels called a label space.

LDP supports two types of label spaces:

Summary Route Propagation

Figure 15-5 shows the summary route propagation between four LSRs in an MPLS network. The LDP discover mechanism is used to periodically transmit LDP hello messages and to signal its desire to advertise label bindings. The LSR sends the LDP hello messages as UDP packets to the well known LDP port (646). The hello messages carry the LDP identifier (ID) of the label space for sending LSR. SalesLSR4 sends a hello packet with the VPI and VCI used to connect to FEC 172.68.0.0. Each LSR then propagates that FEC replacing the VPI and VCI used to connect to its ingress interface.When a labeled packet is being sent from an LSR to its neighbor LSR, the label value carried by the packet is the label value that the egress LSR assigned to represent the FEC of the packet. This causes the label value (VPI/VCI) to be swapped as the packet traverses the network.

LFIB Table Look Up Process

Figure 15-6 shows the packet transmission and LFIB table look up process used between a source and destination over an ATM MPLS network. AdminLSR1 is the ingress point for packets from the router AdminRt1. When the LSR receives the packet it determines the FEC and determines the LSP to use by looking in the LFIB table.

Note   The LFIB table is propagated using the LDP discover mechanism shown in Figure 15-5.

AdminLSR1 adds the label (VPI/VCI) 65,180 to the packet and forwards the packet out ATM interface 0/1/0. The intermediate LSR (NetLSR2) takes the labeled packet and pairs the incoming interface and label and then uses a lookup table to determine the outgoing interface and label. After swapping the incoming label with the new outgoing label the packet is forwarded out to the next LSR.

The label swapping process is continued at each LSR until the last LSR. The egress LSR performs the same look up as the intermediate LSRs but the outgoing label is stripped off and the packet is either routed or switched using Layer 3 to its destination.

MPLS Network Packet Transmission

This section provides a description of a packet being transmitted across an MLPS enabled network and the process used to switch the packets.

When a packet is received at an MPLS ingress interface the interface driver uses the IDB (interface descriptor block) to start the following MPLS process on the packet:

Figure 15-7 shows a packet as it traverse a network from its source on network 130.0.0.0 to its destination on network 180.0.0.0.

The packet from network 130.0.0.0 enters router AdminRt1 at Ethernet interface 2/3 with a destination IP address on network 180.0.0.0. The router preforms a standard routing table lookup and determines the packet should be routed out ATM interface 0/0 to the next hop interface 140.0.0.1 on interface ATM 1/0/0. By using CEF (Cisco Express Forwarding) the Layer 3 switched packet interface FIB (forwarding information base) is queried and the next hop is determined to be out through ATM MPLS interface 3/0/0. Prior to transmission to the next LSR an MPLS label (or VPI/VCI) is appended to the packet just before the destination IP address.

From this point on through the MPLS network, the only information that is checked by the successive LSRs is the label information in the packet. When the packet reaches the edge LSR the MPLS label is popped off and subsequent switching is completed using Layer 3 and standard routing practices.

Configuring Label Edge Routing

This section describes label edge router (LER) for the Cisco Catalyst 8540. With LER, the Cisco Catalyst 8540 can be installed at the edge of a packet- and cell-based network with both or either of them MPLS-enabled. LER also supports multiple TVCs to the same destination prefix and allows a TVC to be selected based upon the CoS value in the incoming label or ToS in the IP packet. The enhanced ATM router module (ARM) serves as the proxy interface for every incoming and outgoing ATM interface (that is linked to an Enhanced ATM router module using the mpls-forwarding command) in the LSP path to do the MPLS packet processing. To enable LER functionality, you must first configure tag switching on an ATM interface and link the ATM interface to an ATM router module for MPLS packet processing. For more information on configuring MPLS on ATM interfaces, refer to "Configuring Tag Switching" in the ATM Switch Router Software Configuration Guide. For more information on configuring MPLS on Ethernet interfaces, refer to "Configuring Tag Switching" in the Layer 3 Switching Software and Feature Configuration Guide.

LER Software Limitations

The following restrictions apply to LER on the Cisco Catalyst 8540:

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Note    To change SDM SRAM configuration you must use the sdm size configuration command and the reload command to reconfigure the memory and then halt and perform a cold restart of the switch.

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MPLS Processing

To configure LER with the enhanced ATM router module acting as MPLS edge proxy, perform the following steps:

Note   You must enable MPLS on the ATM interface by using the mpls ip command.

Note   Once MPLS is enabled on an ATM interface and the interface is linked to the enhanced ATM router module, all head-end, control, and tail-end VCs through that ATM interface terminate on the Enhanced ATM router module. All MPLS or IP packet processing is performed on the linked Enhanced ATM router module.

Note   If you attempt to link an already linked ATM interface to another enhanced ATM router module interface, an error message similar to the following results: ATM <x/x/x> is already functioning as mpls edge for ATM <y/y/y>.

Note   If you attempt to unlink an ATM interface that is not linked, an error message similar to the following results: ATM <x/x/x> is not linked to ATM <y/y/y>.

Example

The following example shows how to link an ATM interface to an enhanced ATM router module interface for LER MPLS functionality:

Tag Switching Processing

To configure LER with the enhanced ATM router module acting as a tag edge proxy, perform the following steps:

Note   You must enable tag switching on the ATM interface by using the tag-switching ip command.

Note   Once tag switching is enabled on an ATM interface and the interface is linked to the enhanced ATM router module, all head-end, control, and tail-end VCs through that ATM interface terminate on the enhanced ATM router module. All MPLS/IP packet processing is performed on the linked enhanced ATM router module.

Note   If you attempt to link an already linked ATM interface to another enhanced ATM router module interface, an error message similar to the following results: ATM <x/x/x> is already functioning as mpls edge for ATM <y/y/y>.

Note   If you attempt to unlink an ATM interface that is not linked, an error message similar to the following results: ATM <x/x/x> is not linked to ATM <y/y/y>.

Example

The following example shows how to link an ATM interface to an enhanced ATM router module interface for LER MPLS functionality:

MPLS Over Fast Ethernet Interfaces

This section describes how to configure MPLS on Fast Ethernet interfaces. By linking a Fast Ethernet interface to an enhanced ATM router module interface, tag or MPLS switching can be enabled on Fast Ethernet interfaces and Fast Ethernet interfaces can be part of a VPN. The enhanced ATM router module (ARM) serves as the MPLS processor on behalf of the Fast Ethernet card. The Fast Ethernet interface forwards all MPLS packets it receives to the enhanced ATM router module. It also forwards all IP packets to the enhanced ATM router module if a VRF is configured on the Fast Ethernet or if the outgoing interface is MPLS-enabled. The enhanced ATM router module processes the packets and forwards them to the appropriate outgoing port.

Note   IPX routing and MPLS processing are incompatible. You must remove all IPX routing configuration from the Fast Ethernet interface with which you wish to link, and from all Fast Ethernet interfaces on the interface module controlled by the same Ethernet processor interface, before configuring MPLS. Each Ethernet processor interface controls four Fast Ethernet interfaces on the interface module. On a 16-port Fast Ethernet interface module, ports 0 through 3 are controlled by one Ethernet processor interface, ports 4 through 7 by another, and so forth. For example, if you want to configure an MPLS control link on Fast Ethernet interface 3/0/1, you must remove all IPX configuration from interfaces 3/0/0, 3/0/1, 3/0/2, and 3/0/3.

Configuring MPLS on Fast Ethernet Interfaces

To configure a MPLS for a Fast Ethernet interface, perform the following steps:

Example

The following example shows how to configure a Fast Ethernet interface and link it to the enhanced ATM router module for processing:

MPLS configuration on a Fast Ethernet interface has the following software restrictions:

MPLS VPNs

This section describes how to configure MPLS VPNs on the ATM switch router.

When used with MPLS, the VPN feature allows several sites to interconnect transparently through a service provider network. One service provider network can support several different IP VPNs. Each of these networks appears to the users as a private network, separate from all other networks. Within a VPN, each site can send IP packets to any other site in the same VPN.

Each VPN is associated with one or more VPN routing or forwarding instances (VRFs). A VRF consists of an IP routing table, a derived Cisco express forwarding (CEF) table, and a set of interfaces that use this forwarding table.

The ATM switch router maintains a separate routing and CEF table for each VRF. This prevents information being sent outside the VPN and allows the same subnet to be used in several VPNs without causing duplicate IP address problems.

For additional MPLS configuration documentation, refer to the sources in Table 15-10.

This section describes how to configure MPLS VPNs on Fast Ethernet and ATM interfaces. By linking the interface to an enhanced ATM router module interface, tag switching can be enabled on the interfaces and they can be part of a VPN Network. The enhanced ATM Router Module (ARM) serves as the MPLS processor on behalf of the interfaces. The VPN interfaces forward all IP packets they receive from the CE device to the enhanced ATM router module. The enhanced ATM router module processes the packets and forwards them to the appropriate outgoing port.

Note   IPX routing and VPN processing are incompatible. You must remove all IPX routing configuration from the Fast Ethernet interface with which you wish to link, and from all Fast Ethernet interfaces on the interface module controlled by the same Ethernet processor interface, before configuring VPN. Each Ethernet processor interface controls four Fast Ethernet interfaces on the interface module. On a 16-port Fast Ethernet interface module, ports 0 through 3 are controlled by one Ethernet processor interface, ports 4 through 7 by another, and so forth. For example, if you want to configure an MPLS control link on Fast Ethernet interface 3/0/1, you must remove all IPX configuration from interfaces 3/0/0, 3/0/1, 3/0/2, and3/0/3.

Configuring VPN on Fast Ethernet Interface

To configure a Fast Ethernet interface as part of an MPLS VPN, perform the following steps:

Fast Ethernet Interface Example

The following example shows how to configure the Fast Ethernet interface connected to the customer equipment from the PE ATM switch router and links it to the enhanced ATM router module for processing:

Note   Subinterfaces on a Fast Ethernet interface cannot be linked to enhanced ATM router module interfaces.

Note   MPLS can be configured on the Fast Ethernet interface using the mpls-forwarding interface command and by linking it to an enhanced ATM router module interface using the mpls-forwarding interface command. The enhanced ATM router module interface should be UP for MPLS processing to work.

Note   The enhanced ATM router module provides efficient MPLS processing for four Fast Ethernet interfaces.

Network Configuration Example

Figure 15-8 is an example of an MPLS VPN using ATM switch routers.

Figure 15-8 shows a VPN using the following routers and ATM switch routers:

75k-CE1 Configuration

The configuration of router 75k-CE1, follows:

8540-ATM-PE1 Configuration

The configuration of ATM switch router 8540-ATM-PE1, follows:

8540-ATM-P Configuration

The configuration of ATM switch router 8540-ATM-P, follows:

8540-ATM-PE2 Configuration

The configuration of ATM switch router 8540-ATM-PE2, follows:

75k-CE2 Configuration

The configuration of router 75k-CE2, follows:

Configuring MPLS VPN Using ATM RFC 1483 Interfaces

Defined in RFC 1483, multiprotocol encapsulation over ATM, provides a mechanisms for carrying traffic other than just IP traffic. RFC 1483 specifies two ways to do this:

LLC encapsulation is provided to support routed and bridged protocols. In this encapsulation format, PDUs from multiple protocols can be carried over the same virtual connection. The type of protocol is indicated in the packet SNAP header. By contrast, the virtual connection multiplexing method allows for transport of just one protocol per virtual connection.

To Configure an ATM RFC 1483 MPLS VPN interface on the ATM switch router, perform the following steps:

Note   To configure a VPN on ATM router module multipoint sub-interface, along with the previously mentioned configuration steps you also need to configure a map-list and apply it on the appropriate multipoint subinterface. See "Configuring IP over ATM," section, "Configuring a PVC-Based Map List" section.

Note   To configure a VPN on enhanced ARM interface you can also use the point-to-point subinterface mode instead of the multipoint.

Example

The following example shows how to configure the enhanced ATM router module interface as part of a VPN:

The following example shows how to configure the RFC1483 MPLS VPN interface connected to the customer equipment from the PE ATM switch router and cross connected to the enhanced ATM router module interface:

The following example shows how to configure the RFC 1483 MPLS VPN interface connected to the provider switch from the PE ATM switch router and cross connected to the enhanced ATM router module interface:

Network Configuration Example

Figure 15-9 is an example of an MPLS VPN RFC 1483 network using ATM switch routers.

Figure 15-9 shows an RFC 1483 VPN using the following routers and ATM switch routers:

75k-CE1 Configuration

The configuration of router 75k-CE1, follows:

8540-ATM-PE1 Configuration

The configuration of ATM switch router 8540-ATM-PE1, follows:

8540-ATM-P Configuration

The configuration of ATM switch router 8540-ATM-P, follows:

8540-ATM-PE2 Configuration

The configuration of ATM switch router 8540-ATM-PE2, follows:

75k-CE2 Configuration

The configuration of router 75k-CE2, follows: