traceroute VRF output

JGCisco

Does anyone understand traceroute VRF output? I can't find an explanation of it anywhere. I've found a million web pages that all say the same thing, but nothing is really explained. The output looks like this:

Pesaro# traceroute vrf Customer_B 200.0.4.1
Type escape sequence to abort.
Tracing the route to 200.0.4.1
1 10.1.1.21 [MPLS: Labels 25/28 Exp 0] 464 msec 280 msec 308 msec
2 10.1.1.5 [MPLS: Labels 22/28 Exp 0] 236 msec 572 msec 228 msec
3 200.0.4.1 108 msec * 100 msec

I understand that the Exp 0 is for the experimental bits.

What I want to know is what the label numbers mean. Are 25 and 22 the inside/outside/local label? Why is the second label 28 for both?

Any help would be appreciated.

dtlokee

Yes, the 25/28 are the labels. The 25 would be the IGP label and the 28 would be the VPN label. In the second hop you can see the IGP label 25 was swapped for 22 but the VPN label is the same.

JGCisco

Is it the VPN number, the VRF number, or the Route Distinguisher number? I'm beginning to think it's the RD.

dtlokee

It's the VPN label generated by BGP, not the Route Distingusher or the Route Target. The route target is sent as an extended community of the route and the Route Distingusher is appended to the front of the IPv4 address to ensure it's unique in the routing domain. Like MPLS labels the VPNv4 label is dynamically created, but by the BGP process in this case (the control plane)

Humper

It's a label stack. The first label as dt mentioned is the IGP label which is swapped at each hop by the LSRs to reach the final destination (edge LSR). The second label is used for MPLS VPN which stays the same at each hop (unless it can be changed???) and is used by the edge LSR for the identification of the VPN..


Ahhhh MPLS how I love you...

JGCisco

awesome, Thanks to everyone