This feature module explains how to configure L2VPN Pseudowire Switching, which extends Layer 2 Virtual Private Network (L2VPN) pseudowires across an interautonomous system (inter-AS) boundary or across two separate Multiprotocol Label Switching (MPLS) networks. The feature supports ATM and time-division multiplexing (TDM) attachment circuits (ACs) and Ethernet ACs.
Your software release may not support all the features documented in this module. For the latest feature information and caveats, see 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 document.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to
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Prerequisites for L2VPN Pseudowire Switching
For the Cisco 12000 series routers, the L2VPN Pseudowire Switching feature for Any Transport over MPLS (AToM) is supported on the following engines:
E2
E3
E4+
E5
E6
For engines that do not support this feature, the packets are sent to the software and forwarded through the slow path.
Note
Engines E1 and E4 do not support L2VPN Pseudowire Switching, even in the slow path.
Restrictions for L2VPN Pseudowire Switching
L2VPN Pseudowire Switching is supported with AToM.
Only static, on-box provisioning is supported.
Sequencing numbers in AToM packets are not processed by L2VPN Pseudowire Switching. The feature blindly passes the sequencing data through the xconnect packet paths, a process that is called transparent sequencing. The endpoint provider-edge (PE) to customer-edge (CE) connections enforce the sequencing.
You can ping the adjacent next-hop PE router. End-to-end label switched path (LSP) pings are not supported.
Do not configure IP or Ethernet interworking on a router where L2VPN Pseudowire Switching is enabled. Instead, configure interworking on the routers at the edge PEs of the network.
The control word negotiation results must match. If either segment does not negotiate the control word, the control word is disabled for both segments.
AToM Graceful Restart is negotiated independently on each pseudowire segment. If there is a transient loss of the label distribution protocol (LDP) session between two AToM PE routers, packets continue to flow.
Per-pseudowire quality of service (QoS) is not supported. Traffic engineering (TE) tunnel selection is supported.
L2VPN Pseudowire Switching allows the user to extend L2VPN pseudowires
across two separate MPLS networks or across an inter-AS boundary, as shown in
the two figures below.
L2VPN Pseudowire Switching connects two or more contiguous pseudowire
segments to form an end-to-end multihop pseudowire. This end-to-end pseudowire
functions as a single point-to-point pseudowire.
As shown in the second figure below, L2VPN Pseudowire Switching enables
you to keep the IP addresses of the edge PE routers private across inter-AS
boundaries. You can use the IP address of the Autonomous System Boundary
Routers (ASBRs) and treat them as pseudowire aggregation (PE-agg) routers. The
ASBRs join the pseudowires of the two domains.
L2VPN Pseudowire Switching also enables you to keep different
administrative or provisioning domains to manage the end-to-end service. At the
boundaries of these networks, PE-agg routers delineate the management
responsibilities.
Figure 1
L2VPN Pseudowire Switching in an Intra-AS Topology
Figure 2
L2VPN Pseudowire Switching in an Inter-AS Topology
How Packets Are Manipulated at the L2VPN Pseudowire Switching Aggregation Point
Switching AToM packets between two AToM pseudowires is the same as switching any MPLS packet. The MPLS switching data path switches AToM packets between two AToM pseudowires. The following list explains exceptions:
The outgoing virtual circuit (VC) label replaces the incoming VC label in the packet. New Internal Gateway Protocol (IGP) labels and Layer 2 encapsulation are added.
The incoming VC label time-to-live (TTL) field is decremented by one and copied to the outgoing VC label TTL field.
The incoming VC label EXP value is copied to the outgoing VC label EXP field.
The outgoing VC label "Bottom of Stack" S bit in the outgoing VC label is set to 1.
AToM control word processing is not performed at the L2VPN Pseudowire Switching aggregation point. Sequence numbers are not validated. Use the Router Alert label for LSP Ping; do not require control word inspection to determine an LSP Ping packet.
How to Configure L2VPN Pseudowire Switching
Use the following procedure to configure L2VPN Pseudowire Switching on each of the PE-agg routers. In this configuration, you are limited to two
neighborcommands after entering thel2vficommand.
Before You Begin
This procedure assumes that you have configured basic AToM L2VPNs. This procedure does not explain how to configure basic AToM L2VPNs that transport Layer 2 packets over an MPLS backbone. For information on the basic configuration, see Any Transport over MPLS .
For interautonomous configurations, ASBRs require a labeled interface.
The following example displays output from the showmplsl2transportvc command:
Router# show mpls l2transport vc
Local intf Local circuit Dest address VC ID Status
------------- -------------------------- --------------- ----- ----
MPLS PW 10.0.1.1:100 10.0.1.1 100 UP
MPLS PW 10.0.1.1:100 10.0.1.1 100 UP
The following example displays output from the showvficommand:
Router# show vfi
VFI name: test, type: point-to-point
Neighbors connected via pseudowires:
Router ID Pseudowire ID
10.0.1.1 100
10.0.1.1 100
Configuration Examples for L2VPN Pseudowire Switching
L2VPN Pseudowire Switching in an Inter-AS Configuration Example
Two separate autonomous systems are able to pass L2VPN packets, because
the two PE-agg routers have been configured with L2VPN Pseudowire Switching.
This example configuration is shown in the figure below.
Figure 3
L2VPN Pseudowire Switching in an Interautonomous System
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Feature Information for L2VPN Pseudowire Switching
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 1
Feature Information for L2VPN Pseudowire Switching
This feature configures L2VPN Pseudowire Switching, which extends L2VPN pseudowires across an interautonomous system (inter-AS) boundary or across two separate MPLS networks.
In Cisco IOS Release 12.2(28)SB, support was added for the Cisco 7200 and 7301 series routers.
In 12.2(33)SRD2, support was added for ATM and TDM ACs.
The following commands were introduced or modified:
l2vfipoint-to-point,neighbor(L2VPN Pseudowire Switching),
showvfi.
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