large icmp packet issue

Robert Bonomi bonomi at mail.r-bonomi.com
Sat Sep 25 22:18:07 CDT 2010


> From nanog-bounces+bonomi=mail.r-bonomi.com at 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 at gmail.com>
> To: nanog at 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.





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