level3.net in Chicago - high packet loss?!?

Wed Sep 7 11:46:46 UTC 2005

On Wed, 7 Sep 2005, Christopher L. Morrow wrote:

> On Tue, 6 Sep 2005 sdb at 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 at 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.... :)

Yeah, it was a sweeping generalisation, hence the excessive use of words
such as "usually" and "most" :)  I was trying to put the point across as
to why things are like this, for those that might be wondering why.  The
main point was actually that the ability of a device (router, web server
etc) to deal with stuff _like_ ICMP message generation does not reflect
its ability to perform it's main task.

> nice to L3 sending in the answer police though :)  Thanks!

Thanks :)

SB

--
Stewart Bamford (Posting as an individual)
Level3 Snr IP Engineer
*** Views expressed are my own and not necessarily those of Level3 ***
Primary email     stewart at whoever.com
Secondary email   me at stewartb.com
Personal website  http://www.stewartb.com/