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

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.

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 inter-Autonomous configurations, ASBRs require a labeled interface.

Note	In this configuration, you are limited to two neighborcommands after entering the l2 vficommand. >

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}

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 

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