[15509] in North American Network Operators' Group
Re: Can you explain why paths to same host diverge?
daemon@ATHENA.MIT.EDU (Mark Boolootian)
Fri Feb 27 23:55:41 1998
From: Mark Boolootian <booloo@cats.ucsc.edu>
To: jhawk@bbnplanet.com (John Hawkinson)
Date: Fri, 27 Feb 1998 20:52:08 -0800 (PST)
Cc: nanog@merit.edu
In-Reply-To: <199802280111.UAA27020@all-purpose-gunk.near.net> from "John Hawkinson" at Feb 27, 98 08:11:48 pm
John,
Thanks very much for providing the cogent explanation.
You ask:
>I feel obligated to ask -- is there some reason you didn't
>direct your query to Sprint, before asking NANOG? It really seems like
>this is the kind of question they should be able to answer for you,
>and diagnose the problem to some extent. I can't see a good reason to ask
>here without asking the providers in question, first.
There were really two reasons I asked this question here. First, it
seemed like an interesting operational issue that I hadn't ever seen
beaten to death on NANOG. Everyone is used to asymmetry between forward
and reverse paths, but I don't think I'd ever seen a case of asymmetry
in the forward path (at least, not while the network was stable). Second,
I don't necessarily expect my provider to tell me why things route the way
they do; I only expect them to fix things when they're broken. NANOG
seems the appropriate place to ask the "why" questions. For what it's
worth, I am pursuing this with our provider.
>It is worth noting, I suppose, that optioned packets (i.e. traceroute -g
>or ping -R) are not CEF-switched, and therefore cannot be used to
>instrument the behavior of this hash. As a result, your best bet is
>limited ttl probes to various hops.
Presumably this is why the reverse traceroutes I ran didn't seem to
shed any light.
Thanks again for the end2end-interest pointer and the fine explanation.
regards,
mb
--
Mark Boolootian
booloo@cats.ucsc.edu
