easy way to scan for issues with path mtu discovery?

Frank Bulk - iNAME frnkblk at iname.com
Tue Jun 24 09:57:47 CDT 2008


Look at mturoute: http://www.elifulkerson.com/projects/mturoute.php

Frank

-----Original Message-----
From: Darden, Patrick S. [mailto:darden at armc.org] 
Sent: Tuesday, June 24, 2008 9:28 AM
To: nanog at nanog.org
Subject: easy way to scan for issues with path mtu discovery?

Hi all,

Does anyone know of an easy way to scan for issues with path mtu discovery
along a hop path?  E.g. if you think someone is ICMP black-holing along a
route, or even on the endpoint host, could you use some obscure nmap flag to
find out for sure, and also to identify the offending hop/router/host?  What
tool would you use to test for this, and how would you do such a test?  Is
there any probing tool that does checks like this automatically?

Seems to me this happens often enough that someone has probably already
figured it out, so I am trying not to reinvent the wheel.  All I can think
of would be to handcraft packets of steadily increasing sizes and look for
replies from each hop on the route (which would be laborious at best).
Google has not been kind to my researches so far.

I appreciate any help!
--Patrick Darden






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