netdev - Re: [PATCH net-next] ipv4: introduce new IP_MTU_DISCOVER mode IP_PMTUDISC

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Message-Id: <20131029.153838.825609236199228090.davem@davemloft.net>
Date:	Tue, 29 Oct 2013 15:38:38 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	fweimer@...hat.com
Cc:	hannes@...essinduktion.org, netdev@...r.kernel.org
Subject: Re: [PATCH net-next] ipv4: introduce new IP_MTU_DISCOVER mode
 IP_PMTUDISC_INTERFACE

From: Florian Weimer <fweimer@...hat.com>
Date: Tue, 29 Oct 2013 08:36:35 +0100

> You could make the path MTU dependent on the protocol (which would
> even be the correct solution from a technical point of view) and use
> validation for TCP and UDP, but that's a fairly invasive change for
> such relatively minor functionality.

The code pretty much already does this, we cannot even find the
exact route without being able to look up the socket right now.
We need the full flow info.

There is a backup path, but you could make the new (non-default)
behavior be to never trust that path for protocols like UDP and
TCP.

I don't buy any of your arguments against my suggestions so far.
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