netdev - Re: [PATCH net-next] ipv4: introduce ip_dst_mtu_secure and protect forwarding path against pmtu spoofing

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Date:	Thu, 19 Dec 2013 00:12:03 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	hannes@...essinduktion.org
Cc:	johnwheffner@...il.com, netdev@...r.kernel.org,
	eric.dumazet@...il.com
Subject: Re: [PATCH net-next] ipv4: introduce ip_dst_mtu_secure and protect
 forwarding path against pmtu spoofing

From: Hannes Frederic Sowa <hannes@...essinduktion.org>
Date: Thu, 19 Dec 2013 01:07:59 +0100

> On Wed, Dec 18, 2013 at 06:55:13PM -0500, John Heffner wrote:
>> On using the interface MTU for all forwarded packets, I have a similar
>> reaction as David.  And why are forwarded packets more special than
>> local ones, from the routing code's point of view?  It seems like
>> there could be other ways to harden a router, like firewall rules.
> 
> I doubt it is trivial to set up such a filter as we have to inspect
> the payload of the icmp error. I played with it and it is certainly
> possible, but my intention was that the networking stack does try to
> prevent fragmentation and delay generation of fragments to the last
> router on the path where it is necessary.

John's more important point is why treat forwarded traffic specially
from that which is locally generated?
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