[98368] in North American Network Operators' Group
Re: large organization nameservers sending icmp packets to dns servers.
daemon@ATHENA.MIT.EDU (Valdis.Kletnieks@vt.edu)
Mon Aug 6 13:48:16 2007
To: "Steven M. Bellovin" <smb@cs.columbia.edu>
Cc: Drew Weaver <drew.weaver@thenap.com>,
"'nanog@merit.edu'" <nanog@merit.edu>
In-Reply-To: Your message of "Mon, 06 Aug 2007 12:13:03 EDT."
<20070806161304.0BABB7660C3@berkshire.machshav.com>
From: Valdis.Kletnieks@vt.edu
Date: Mon, 06 Aug 2007 13:37:06 -0400
Errors-To: owner-nanog@merit.edu
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On Mon, 06 Aug 2007 12:13:03 EDT, "Steven M. Bellovin" said:
> > 1) ICMP is handled at the same rate as TCP/UDP packets in all the
> > routers involved (so there's no danger of declaring a path "slow"
> > when it really isn't, just becase a router slow-pathed ICMP).
>
> This is aimed at hosts, not routers, right? As far as I know, routers
> don't slow-path forwarded ICMP. Hosts will probably reply to ICMP from
> their kernel, so it's a faster response than a user-level DNS reply.
Well, they don't *directly* slow-path it. But we've seen *plenty* of cases
of "multi-hop performance as indicated by ICMP Echo Request/Reply doesn't at
all match throughput/latency as indicated by TCP-level stats" mentioned on
this list...
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