Re: [mpls-linux-general] Cisco traceroute issues

[James R. L. <jl...@mi...>]

This is good info.  When you do not set 'mpls ip propagate-ttl' the LDP
lsp from PE1-PE2 is being treated as one hop, therefore mpls-linux is
not seeing a MPLS packet with a TTL of 1, so it is not really participating
the trace route (you'll never see it in the hop list).

By setting 'mpls ip propagate-ttl' the P router will 'participate in
the traceroute' and will see a MPLS packet with TTL 1.  In this case
what do you expect to happen?  If you are tracing from CE1-CE2, P does
not know about the IP space associated with the CE routers, so it
cannot generate a ICMP message.  One option (which I think Cisco implements)
is to generate a ICMP message, and forward it to the end of the LSP
and let the egress (PE2 in this case) handle forwarding it back to CE1.

Either way, mpls-linux should not crash when faced with this situation
I'll fix that.

If you wouldn't mind.  Could you submit a bug report at
http://sf.net/projects/mpls-linux/?

Thank you

On Mon, Mar 10, 2003 at 11:07:35AM -0600, Ben Groff wrote:
> 
> 
> I have a test network setup using two Cisco 2610 routers running IOS
> version 12.2(8)T5.  These routers are configured as PE routers with a CE
> router attached to each 2610.  The PE routers have a MPLS-VPN configured
> with MP-BGP and can successfully pass traffic from the CE to the other CE.
> I have verified that the label stacks are functioning correctly. I have a
> linux box running the latest public release version of mpls-linux, ldp,
> and zebra 0.93a.  The linux box is acting as a P router.
> 
> The lab setup looks something like this:
> 
>              CE1 -- PE1 -- P -- PE2 -- CE2
> 
> 
> Everything works fine in this setup until I run a traceroute on the CE
> towards the other CE.  When I do this, the linux box will lock hard.
> There are no crash messages, no kernel panics, just completely frozen.  I
> managed to trace the issue to the following command on the cisco routers:
> mpls ip propagate-ttl.  When I disable that command, the traceroute works
> fine.  I can reproduce this problem at will.  Is there any further
> information you all would like to see in regards to this issue?
> 
> Thanks,
> -Ben
> 
> 
> 
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-- 
James R. Leu