MPLS L2 VPN(VPWS) Tunnel Label and VC Label

[TangoAlfa]

In MPLS L2 VPN (AToM and VPWS) referring to the diagram here IGP is running OSPF with MPLS Backbone. And R1 and R2 connected with Pseudo Wire. Now when user 192.168.0.100 ping to Server 192.168.0.101 the first packet is  going with only one Label but the return packet is coming with Tunnel and VC label both. Why so ? And how to check the VC label and tunnel Label? (ref: capture snap below)

[Harold Ritter · Accepted solution]

Hi @TangoAlfa ,

> the first packet is  going with only one Label but the return packet is coming with Tunnel and VC label both. Why so ?

This is a consequence of the penultimate hop popping (PHP) and the place where the sniffer trace was taken from. From the output you provided, the sniffer trace was taken from the segment between  LSR-P-R-2 and LER-PE-R-2, at which point the top label had already been popped for the traffic coming from LER-PE-R-1.

If you want to see both labels for both the icmp request and icmp reply, you should take the sniffer trace from the segment between LSR-P-R-1 and LSR-P-R-2. 

Regards,

[TangoAlfa]

Ohhhhhhh I missed...

@Harold Ritter You are great. Thanks you are right...

Now Can you please help me one additional part that, the VC Label is dedicated to each AC of PE router router right?

And how to check which one the VC label and which one is the tunnel Label?

Great

[Harold Ritter]

Hi @TangoAlfa ,

You can use "sh mpls l2 binding" from the PE to see the local and remote labels for each VC.

You can also use "show ip cef <remote PE loopback IP address>" from the PE to see the IGP label that will be used to forward packets to the other PE.

You can use "show mpls forwarding" on the P router to see how traffic with a given IGP label will be forwarded.

Regards,

[TangoAlfa]

Tunnel Label Push Swap and Pop but Does VC Label Swap ?

[Harold Ritter]

Hi @TangoAlfa ,

There is no label swap for the VC label. The VC label is just used on the PE to bind the L2 frames to the attachment circuit (AC). Only the IGP label will be swapped on the P routers.

Regards,