easy way to scan for issues with path mtu discovery?

Justin Shore justin at justinshore.com
Tue Jun 24 14:49:53 UTC 2008

Darden, Patrick S. wrote:
> 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.

Take a look at tracepath.


I haven't done much of anything with it but it may be of use to you.


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