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To: "Carlos Velasco" <carlosev@newipnet.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: 2.4.20 Broken Path MTU Discovery?
References: <200302021958160177.2A4B5622@192.168.128.16.suse.lists.linux.kernel>
From: Andi Kleen <ak@suse.de>
Date: 03 Feb 2003 01:29:51 +0100
In-Reply-To: "Carlos Velasco"'s message of "2 Feb 2003 20:03:18 +0100"
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"Carlos Velasco" <carlosev@newipnet.com> writes:
> 
> ?May be the Linux box is giving up PMTU? ?Why? it now knows MTU is 400.
> I have others windows boxes in the network, they work fine with PMTU.

A MTU of 400 is illegal, IPv4 requires a minimum MTU of 576 bytes. Below
it linux uses the minimum MTU and turns off path mtu discovery (=
drops DF)

You can change that minimum mtu by changing the ip_rt_min_pmtu variable
(no sysctl, you have to change it in /dev/kmem or recompile) 

-Andi
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