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New Member

no mpls ip propagate-ttl

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

1 ACCEPTED SOLUTION

Accepted Solutions
Cisco Employee

no mpls ip propagate-ttl

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

Thanks,

Luc

3 REPLIES
Cisco Employee

no mpls ip propagate-ttl

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

New Member

no mpls ip propagate-ttl

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.

Cisco Employee

no mpls ip propagate-ttl

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

Thanks,

Luc

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