no mpls ip propagate-ttl

[Luciano Vigano']

Hi all,

a strange behaviour occours with the MPLS labels and the trace command.

This is the output of the trace from CE2 to CE1:

CE2#traceroute 20.20.20.1

Type escape sequence to abort.

Tracing the route to 20.20.20.1

  1 10.10.10.13 28 msec 4 msec 8 msec

  2 10.10.10.9 [MPLS: Labels 16/20 Exp 0] 64 msec 76 msec 72 msec

  3 10.10.10.2 [MPLS: Label 20 Exp 0] 52 msec 68 msec 24 msec

  4 10.10.10.1 72 msec 84 msec 72 msec

After apply "no mpls ip propagate-ttl" on both PE and P here the same trace:

CE2#traceroute 20.20.20.1

Type escape sequence to abort.

Tracing the route to 20.20.20.1

  1 10.10.10.13 32 msec 28 msec 28 msec

  2 10.10.10.2 [MPLS: Label 20 Exp 0] 80 msec 100 msec 88 msec

  3 10.10.10.1 128 msec 120 msec 120 msec

Is it a normal behaviour ?

Regards,

Luciano

[Luc De Ghein]

Hi,

Yes, this is normal. When the no mpls ip propagate-ttl command is applied on the igress PE, the P routers will not see the TTL expire of the traceroute packets. The whole point of this command is to hide the core (P routers) from the traceroute command.

Thanks,

Luc

[Luciano Vigano']

Ciao Luc,

thanks for your quick and kind answer.

Is there any way to completely hide the MPLS label?

If I take a trace towards our carriers (MPLS VPN, no TE) I can see the CE and the PE hop but not the MPLS label ?

Ciao!

L.

[Luc De Ghein · Accepted solution]

No way to completely remove all labels, in all cases.

Thanks,

Luc