large icmp packet issue

Robert Bonomi bonomi at
Sun Sep 26 03:18:07 UTC 2010

> From at  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>
> To: nanog at
> 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.

More information about the NANOG mailing list