MPLS: Layer 2 VPNs Configuration Guide, Cisco IOS XE Release 3S

L2VPN Pseudowire Switching

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.

Finding Feature Information

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 for L2VPN Pseudowire Switching" section.

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

Contents

•Restrictions for L2VPN Pseudowire Switching

•Information About L2VPN Pseudowire Switching

•How to Configure L2VPN Pseudowire Switching

•Configuration Examples for L2VPN Pseudowire Switching

•Additional References

•Feature Information for L2VPN Pseudowire Switching

Restrictions for L2VPN Pseudowire Switching

•In Cisco IOS XE Release 2.4, Pseudowire Switching is supported on Ethernet over MPLS attachment circuits.

•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 PE-CE connections enforce the sequencing.

•You can ping the adjacent next-hop PE router. End-to-end 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 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.

•Attachment circuit interworking is not supported.

Information About L2VPN Pseudowire Switching

To configure the L2VPN Pseudowire Switching feature, you should understand the following concepts:

•How L2VPN Pseudowire Switching Works

•How Packets Are Manipulated at the L2VPN Pseudowire Switching Aggregation Point

How L2VPN Pseudowire Switching Works

L2VPN Pseudowire Switching allows the user to extend L2VPN pseudowires across an inter-AS boundary or across two separate MPLS networks, as shown in Figure 1 and Figure 2. 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 Figure 2, 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 to1.

•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

This section explains how to perform the following tasks:

•Configuring L2VPN Pseudowire Switching

Configuring L2VPN Pseudowire Switching

Use the following procedure to configure L2VPN Pseudowire Switching on each of the PE-agg routers.

Prerequisites

•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 inter-Autonomous configurations, ASBRs require a labeled interface.

Restrictions

In this configuration, you are limited to two neighbor commands after entering the l2 vfi command.

SUMMARY STEPS

1. enable

2. configure terminal

3. l2 vfi name point-to-point

4. neighbor ip-address vcid encapsulation mpls | pw-class pw-class-name

5. exit

6. exit

7. show mpls l2transport vc [vcid [vc-id | vc-id-min vc-id-max]] [interface name [local-circuit-id]] [destination ip-address | name] [detail]

8. show vfi [vfi-name]

9. ping [protocol] [tag] {host-name | system-address}

DETAILED STEPS

show mpls l2transport vc [vcid [vc-id | 
[vc-id-min vc-id-max]] [interface name 
[local-circuit-id]] [destination ip-address | 
name] [detail]

Router# show mpls l2transport vc

show vfi [vfi-name]

Router# show vfi atomtunnel

ping [protocol] [tag] {host-name | 
system-address} 

Router# ping 10.1.1.1

Examples

The following example displays the output of the show mpls l2transport vc 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 the output of the show vfi command:

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

This section provides the following configuration example:

•L2VPN Pseudowire Switching in an Inter-AS Configuration: Example

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 Figure 3.

Figure 3 L2VPN Pseudowire Switching in an InterAutonomous System

Additional References

The following sections provide references related to L2VPN Pseudowire Switching.

Related Documents

Standards

MIBs

RFCs

Technical Assistance

Feature Information for L2VPN Pseudowire Switching

Table 1 lists the features in this module and provides links to specific configuration information.

Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which Cisco IOS XE software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.

Note Table 1 lists only the Cisco IOS XE software release that introduced support for a given feature in a given Cisco IOS XE software release train. Unless noted otherwise, subsequent releases of that Cisco IOS XE software release train also support that feature.

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