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Re: level3.net in Chicago - high packet loss?!?
On Wed, 7 Sep 2005, Christopher L. Morrow wrote: > On Tue, 6 Sep 2005 email@example.com wrote: > > > On Tue, 6 Sep 2005, Christopher L. Morrow wrote: > > > > > On Tue, 6 Sep 2005, chip wrote: > > > > > > > On 9/6/05, Joe Maimon <firstname.lastname@example.org> 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 email@example.com Secondary email firstname.lastname@example.org Personal website http://www.stewartb.com/