[j-nsp] MPLS labels on a traceroute across an IXP?

[Darius Jahandarie]

On Mon, Nov 5, 2012 at 3:10 PM, Gavin Henry <ghenry at suretec.co.uk> wrote:
> Now I've never seen:
>
> MPLS Label=9814 CoS=0 TTL=1 S=1
>
> on a traceroute before (being new to MPLS too :-) ) and presume it's
> showing because of the junos traceroute, whereas I don't see it from
> the same
> network on a linux box?

Yes. You need to use the -e flag if you want it to show on a Linux traceroute.

> My other question is should this actually show and not be remove by
> the egress LER?

Without ICMP extensions, when an LSR receives an undeliverable
MPLS-encapsulated datagram, it strips the MPLS label stack and punts
that IP datagram to the error processing module, which then generates
the, e.g., Time Exceeded ICMP.

With ICMP extensions, the LSR instead provides the MPLS label stack to
the error processing module, which appends that information to the
ICMP using a "MPLS Label Stack Object".

So, as long as the router received the datagram as MPLS, it can/will
send back the ICMP with a MPLS Label Stack Object. This applies to an
LER.

-- 
Darius Jahandarie