[84164] in North American Network Operators' Group
Re: level3.net in Chicago - high packet loss?!?
daemon@ATHENA.MIT.EDU (Christopher L. Morrow)
Tue Sep 6 22:03:55 2005
Date: Wed, 07 Sep 2005 02:01:20 +0000 (GMT)
From: "Christopher L. Morrow" <christopher.morrow@mci.com>
In-reply-to: <Pine.LNX.4.58.0509062059560.4914@eaton.stewartb.com>
To: nanog <nanog@merit.edu>
Errors-To: owner-nanog@merit.edu
On Tue, 6 Sep 2005 sdb@stewartb.com wrote:
>
> On Tue, 6 Sep 2005, Christopher L. Morrow wrote:
>
> > On Tue, 6 Sep 2005, chip wrote:
> >
> > > On 9/6/05, Joe Maimon <jmaimon@ttec.com> wrote:
> > > >
> > > >
> > > > If the hop(s) following the one you see loss for shows no loss, then
> > > > disregard the loss for that hop, obviously whatever it is, it does not
> > > > affect transit, which is what you really want to know.
> > > >
> > > > Is that correct?
> > > >
> > > This is one of the most misunderstood concepts in properly reading output
> > > from a traceroute (mtr, visualtraceroute, whatever). Basically you are
> > > seeing loss of packets destined directly *TO* that router, not THRU it. Most
> >
> > no... not destined TO the router, destined THROUGH the router that happen
> > to TTL=0 ON that router.
>
> Very true. Most backbone kit on a tier 1 network is designed to switch
I was really just pointing out that 'traceroute' or 'mtr' send packets
with increasing TTL to show 'loss' or 'delay' from place to place, I
wasn't trying to debate the every-changing reasons why backbone equipment
might or might not answer 'ttl-expired' or 'unreachable' (or any
'exception traffic' really) in a 'timely' fashion. That issue changes with
the wind/os/hardware/model.... :)
nice to L3 sending in the answer police though :) Thanks!
-Chris
