[93133] in North American Network Operators' Group
Re: ICMP & PathMTU
daemon@ATHENA.MIT.EDU (Florian Weimer)
Fri Oct 27 08:25:02 2006
From: Florian Weimer <fw@deneb.enyo.de>
To: Jim Popovitch <jimpop@yahoo.com>
Cc: nanog@merit.edu
Date: Fri, 27 Oct 2006 14:05:49 +0200
In-Reply-To: <1161916157.3487.4.camel@localhost> (Jim Popovitch's message of
"Thu, 26 Oct 2006 22:29:17 -0400")
Errors-To: owner-nanog@merit.edu
* Jim Popovitch:
> Two questions for everybody...(any and all responses appreciated, even
> if the reply mentions botnets or hammers ;-) )
>
> 1) What value is ICMP if everybody pretty much considers it's accuracy
> suspect?
The problem with ICMP-based traceroutes is that it doesn't necessarily
test the path you are interested in. Use tcptraceroute or traceproto
instead.
Of course, this doesn't solve the problem that TTL Exceeded messages
might be generated with very low priority, which is in generally a
very good idea.
> 2) How does ICMP's suspect nature affect Path MTU?
In this case, you're interested in the ICMP payload, not the fact
whether an ICMP packet goes through or not. (You lose if someone
filters ICMP, though.)
