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

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Message-Id: <20131031.002911.1316728367651608156.davem@davemloft.net>
Date:	Thu, 31 Oct 2013 00:29:11 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	hannes@...essinduktion.org
Cc:	netdev@...r.kernel.org, fweimer@...hat.com
Subject: Re: [PATCH net-next] ipv4: introduce new IP_MTU_DISCOVER mode
 IP_PMTUDISC_INTERFACE

From: Hannes Frederic Sowa <hannes@...essinduktion.org>
Date: Wed, 30 Oct 2013 23:58:51 +0100

> DNS resolver can fallback to TCP for querying where we can honour the
> path MTU because it won't do any harm and ensures connectivity.
> 
> Also for TCP the socket is matched on the whole 4-tuple and we may
> fallback to a 2-tuple lookup on unconnected UDP sockets. The new socket
> option would let an application programmer choose to do path mtu discovery
> because it knows it will only use a connected socket. On unconnected
> sockets one can specify IP_PMTUDISC_INTERFACE to suppress the path MTU
> updates and always use the interface MTU without the DF-bit set.

This still sounds like a route scope policy with two binary states,
one for connected sockets and one for unconnected ones.
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