[c-nsp] traceroute shows mpls labels...how?

[Aaron]

Thanks Roger, I knew about that.  But what I was asking is how does that
label information get reported back to the device that I'm doing the
traceroute from....  you see what I'm asking ? 

I might put a sniffer on the device that I'm tracing from to look at that
icmp ttl expired in transit packets and see where exactly is that label
information embedded/carried in the ttl expired in transit packets..... see
what I'm asking ?

Aaron


-----Original Message-----
From: Roger Wiklund [mailto:roger.wiklund at gmail.com] 
Sent: Wednesday, August 22, 2012 2:49 PM
To: Aaron
Cc: cisco-nsp at puck.nether.net
Subject: Re: [c-nsp] traceroute shows mpls labels...how?

MPLS TTL

By default mpls ip propagation-ttl is enabled in global configuration mode.
This enabled user to trace the hops of the mpls router with labels as shown
in above traceroute. This is because MPLS TTL field is copied from IP TTL
field, on each MPLS LSR hop a TTL will be decremented.

To "hide" the MPLS hops you can disable it by doing no mpls ip
propagation-ttl on every LSR in global configuration mode. Disabling MPLS
propagation TTL will make MPLS TTL field to have a fixed 255 value, and on
every MPLS LSR hop the IP TTL value will be intact. IP TTL will only be
decremented when egress LSR sends out to the destination host unlabeled.

m1(config)#no mpls ip propagate-ttl

Not sure why you're not seeing it in Windows, prob a very simple traceroute
implementation.

/Roger

On Wed, Aug 22, 2012 at 9:21 PM, Aaron <aaron1 at gvtc.com> wrote:
> Do you all know how this works?  How is traceroute able to report back 
> the mpls label that is in use in the transit hops?  Also wondering why 
> I don't see this on windows command line tracert
>
>
>
> Aaron
>
>
>
>
>
> RP/0/RSP0/CPU0:9k#trace vrf one 1.2.3.4 source 2.4.6.8
>
>
>
> 1  19.1911.5 [MPLS: Labels 16001/16220 Exp 0] 2 msec  1 msec  0 msec
>
> 2  19.1911.1 [MPLS: Label 16220 Exp 0] 0 msec  0 msec  1 msec
>
> 3  88.88.191.22 0 msec  0 msec
>
>     19.1911.33 1 msec
>
> 4  88.88.191.18 1 msec  1 msec  0 msec
>
> 5  88.88.135.221 10 msec  10 msec  11 msec
>
> 6  122.47.236.130 [MPLS: Label 17039 Exp 1] 47 msec  49 msec  51 msec
>
> 7  122.47.154.53 [MPLS: Labels 0/17017 Exp 1] 48 msec  49 msec  47 
> msec
>
> 8  122.45.30.134 [MPLS: Labels 23417/17016 Exp 1] 48 msec  49 msec  47 
> msec
>
> 9  122.45.1.17 [MPLS: Labels 23439/17016 Exp 1] 50 msec  49 msec  51 
> msec
>
> 10 122.45.31.189 [MPLS: Labels 0/17016 Exp 1] 51 msec  54 msec  51 
> msec
>
> 11 122.45.158.34 [MPLS: Labels 0/16009 Exp 1] 49 msec  50 msec  47 
> msec
>
> 12 122.45.104.49 46 msec  46 msec  47 msec
>
> 13 122.45.108.14 47 msec  47 msec  47 msec
>
> 14  *  *  *
>
> 15  *  *  *
>
> 16  *
>
>
>
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