Re: Help me make sense of these traceroutes please

[Pedro Cavaca <pmsac.nanog () gmail com>]

On 25 December 2013 00:03, Sam Moats <sam () circlenet us> wrote:

> On 2013-12-24 18:55, Jeroen Massar wrote:
>
> > On 2013-12-25 00:16, Sam Moats wrote:
> >
> > > Hello Nanog community,
> > > I would like to enlist your help with understanding this latency I'm
> > > seeing.
> >
> > You are likely seeing the effects of asymmetric routing.
>
> That's what I was thinking to.
>
>
> > [..]
> >
> > > Tracing route to xxx.yyy.ie [193.1.x.x]
> >
> > www.heanet.ie by chance? :)
>
> Yes they were the owners of the IP I used for the example case and the
> heanet folks are actually totally awesome :-)
>
>
>
> > Though you could use for instance:
> > http://planchet.heanet.ie/toolkit/gui/reverse_traceroute.cgi
> >
> > to do a reverse traceroute, do make sure you force your connectivity to
> > IPv4 as that host will do IPv6 too. (locally nullrouting the destination
> > /128 is the trick I use for 'disabling' IPv6 temporarily).
> >
> > Otherwise the HEANET folks are extremely helpful and clued in, you can
> > always ask them for help with issues. It is the end-of-year though and
> > those Irish folks have lots of really good whiskey, Guinness thus you
> > might have to be patient till the new year.
>
> Also you'd be amazed how many network issues can be solved with a bunch of
> IT folks and an ample supply of Guinness
>
>
>
> > Alternatively, you could use a tool like 'tracepath' or 'mtr' as those
> > reports multiple answers to a response and also check for the TTL on the
> > return packets.
> >
> > Greets,
> >  Jeroen
>
> Thanks, this isn't affecting my service now I've worked around it so it's
> more a curiosity than anything. It seems really odd to me that the same L3
> edge router would route the ICMP unreachable back to me via different paths
> based on the final destination IP of the of the ICMP echo packet.
Based on the data you provided, my guess is some kind of MPLS transport
(please refer to
https://www.nanog.org/meetings/nanog45/presentations/Sunday/RAS_traceroute_N45.pdf,
pages 46-48).

HTH.


> Well its Christmas eve here and the customers are happy so Guinness seems
> like the best approach now :-)
>
> Thanks and have a good Holiday,
> Sam Moats