[130021] in North American Network Operators' Group
Re: large icmp packet issue
daemon@ATHENA.MIT.EDU (Robert Bonomi)
Sat Sep 25 23:20:18 2010
Date: Sat, 25 Sep 2010 22:18:07 -0500 (CDT)
From: Robert Bonomi <bonomi@mail.r-bonomi.com>
To: fedorafans@gmail.com, nanog@nanog.org
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
> From nanog-bounces+bonomi=mail.r-bonomi.com@nanog.org Sat Sep 25 21:56:30 2010
> Date: Sat, 25 Sep 2010 21:57:53 -0500
> Subject: large icmp packet issue
> From: fedora fedora <fedorafans@gmail.com>
> To: nanog@nanog.org
>
> I am having problem getting ping to work to a specific destination host when
> using large size icmp packet and i am hoping someone here can offer some
> suggestion.
>
> With regular ping, i can ping this remote host without any problem, but if i
> crank up the packet size to above 1500 (1500 still works), i won't get any
> icmp reply.
>
> My first thought was this was a pmtu issue. but when I ran tcpdump on this
> remote host, i saw the incoming ping requests and this host actually sent
> back icmp replies, so it appears that there is some device in between
> blocking these large size icmp reply packets.
>
> Here is the question, how can i find out which hop on the path is causing
> this behavior?
Did you consider doing a traceroute?
And then pinging the intermediate machines? with the big packets, that is.
you'll get a response from the 'near side' of the problem, but -not-
from any machine on the far side of it.
Ping with small packets first, to discovr machines that dont respond to
pings at all.
