Tags

In this post we will look at what happens to the TTL value of a packet when it enters the MPLS VPN. We will also see how we can change that behavior to hide the provider network from customers.

C1S1(CE)—R1(PE)—R2(P)—R3(P)—R4(PE)—C1S2(CE)

Before disabling TTL propagation bellow is the trace route:

1 192.168.10.1 20 msec 16 msec 16 msec
2 192.168.12.2 [MPLS: Labels 22/25 Exp 0] 112 msec 112 msec 104 msec
3 192.168.23.2 [MPLS: Labels 22/25 Exp 0] 112 msec 88 msec 84 msec
4 192.168.11.1 [MPLS: Label 25 Exp 0] 76 msec 80 msec 76 msec
5 192.168.11.2 64 msec * 120 msec

After putting no mpls ip propagate-ttl forwarded bellow is the trace route output:

1 192.168.10.1 8 msec 52 msec 20 msec
2 192.168.11.1 [MPLS: Label 25 Exp 0] 88 msec 88 msec 76 msec
3 192.168.11.2 116 msec * 160 msec

It hides the P routers from the client. You need put this command in all your PE and P router.