Date: Tue, 28 Oct 2008 14:02:15 -0700 From: John-Mark Gurney <jmg@funkthat.com> To: Eitan Shefi <eitans@mellanox.co.il> Cc: freebsd-net@freebsd.org Subject: Re: It seems that FreeBSD-7.0 does not use the available MTU Message-ID: <20081028210215.GE51033@funkthat.com> In-Reply-To: <5D49E7A8952DC44FB38C38FA0D758EADCC5FB7@mtlexch01.mtl.com> References: <5D49E7A8952DC44FB38C38FA0D758EADC72E72@mtlexch01.mtl.com> <5D49E7A8952DC44FB38C38FA0D758EADCC5FB7@mtlexch01.mtl.com>
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Eitan Shefi wrote this message on Mon, Oct 27, 2008 at 23:53 +0200:
> I am using 2 hosts with FreeBSD-7.0 connected directly.
> When I change the MTU to a value greater then 1500, for example 3000,
> and then send "ping" with message size 2500, from one host to the other,
> the other host gets more then one ICMP packet, even thaw the message
> that was send is match smaller then the MTU.
>
> I tried to run this test using a different NIC, but I got the same
> behavior.
>
> I run:
> 1. On both hosts:
> ifconfig mtnic0 mtu 3000
> 2. Than on one host I run:
> tcpdump -i mtnic0 icmp
> 3. And on the other host I run:
> ping -s 2500 -c 1 OTHER_HOST_IP (ping to "mtnic0" on the other
> host)
run netstat -rnW to see what the route's MTU is. Most likely you need
to set the mtu before you configure an ip address on the interface so
that the network's route is created w/ the correct MTU...
either readd the network route, or change the mtu of the route for the
host:
route change -mtu 3000 OTHER_HOST_IP
also change it on the network route so that when the host route gets
flushed and recreated it will be created w/ the correct MTU...
--
John-Mark Gurney Voice: +1 415 225 5579
"All that I will do, has been done, All that I have, has not."
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