MPLS/VPN Data Plane?Packet Forwarding

Now that the final configuration is complete, and the VPN routes are propagated across the SuperCom backbone, you can learn how to examine the MPLS label assignment and which labels are present in the label stack.

Figure 9-13 shows a portion of the example topology, which you can use to identify this label assignment. The EuroBank Paris site injects subnet 196.7.25.0/24 into the MPLS/VPN backbone, which is advertised subsequently to the EuroBank San Francisco site. The figure shows the relevant label assignments, and you can see the relevant IOS commands to see these assignments in the examples that follow.

From the perspective of the SuperCom San Jose PE-router, you can see in Example 9-25 that you can use the show ip bgp vpnv4 vrf-name tags command to identify which VPN tag is assigned (by the originating PE-router) to the route. In the example, a tag of 38 is assigned to subnet 196.7.25.0/24. You can see this by examining the Out tag field in the command output.

Example 9-25 show ip bgp vpnv4 vrf-name Command

San Jose# show ip bgp vpnv4 vrf EuroBank tags



   Network          Next Hop      In tag/Out tag

Route Distinguisher: 1:27 (EuroBank)

   10.2.1.0/24      0.0.0.0         38/aggregate(EuroBank)

   196.7.25.0       194.22.15.1     notag/38

The BGP next-hop for the 196.7.25.0/24 subnet is 194.22.15.1, which is the loopback address of the SuperCom Paris PE-router. This next-hop address was learned via the SuperCom IGP and, therefore, the show tag-switching forwarding-table command must be used to identify the IGP label that is used to forward any packets destined for the 196.7.25.0/24 subnet. Example 9-26 shows the output for this command for the SuperCom San Jose router and for the Washington P-router that is in the path to the Paris PE-router. The example also shows the forwarding table for the Paris PE-router and highlights the 196.7.25.0/24 subnet as a VPN route by the [V].

Example 9-26 show tag-switching forwarding-table Command

San Jose# show tag-switching forwarding-table



Local  Outgoing    Prefix            Bytes tag  Outgoing   Next Hop

tag    tag or VC   or Tunnel Id      switched   interface

33     36          194.22.15.1/32       0       AT1/0/0.1  point2point

38     Aggregate   10.2.1.0/24[V]    3120



Washington# show tag-switching forwarding-table



Local  Outgoing    Prefix            Bytes tag  Outgoing   Next Hop

tag    tag or VC   or Tunnel Id      switched   interface

36     Pop tag     194.22.15.1/32       9416    AT0/1/0.1  point2point



Paris# show tag-switching forwarding-table



Local  Outgoing    Prefix            Bytes tag  Outgoing   Next Hop

tag    tag or VC   or Tunnel Id      switched   interface

38     Aggregate   196.7.25.0/24[V]  1040