large icmp packet issue

fedora fedora fedorafans at gmail.com
Sat Sep 25 22:33:31 CDT 2010


Thanks, the thing is

How can i be sure even if a device blocks my ping , it might have policy
blocking ping at it at all.

On Sat, Sep 25, 2010 at 10:18 PM, Robert Bonomi <bonomi at mail.r-bonomi.com>wrote:

> > 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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