netdev - Re: UDP path MTU discovery

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20100401005539.GZ20695@one.firstfloor.org>
Date:	Thu, 1 Apr 2010 02:55:39 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Glen Turner <gdt@....id.au>
Cc:	Rick Jones <rick.jones2@...com>, Andi Kleen <andi@...stfloor.org>,
	netdev@...r.kernel.org
Subject: Re: UDP path MTU discovery

On Thu, Apr 01, 2010 at 10:13:04AM +1030, Glen Turner wrote:
> On Mon, 2010-03-29 at 10:01 -0700, Rick Jones wrote:
> 
> > But which of the last N datagrams sent by the application should be retained for 
> > retransmission?  It could be scores if not hundreds of datagrams depending on 
> > the behaviour of the application and the latency to the narrow part of the network.
> 
> We don't need that sort of exotica from the kernel.  The applications
> have to be prepared to retransmit lost packets in any case.
> 
> What we need is an API for an instant notification that a ICMP Packet
> Too Big message has arrived concerning the socket.

That already exists of course: IP_RECVERR

> As for David Miller's rant, the applications currently have no choice
> but to "do it stupidly" as the kernel doesn't pass enough information
> for user space to do it intelligently.  If the kernel passed user space
> the same indication as TCP gets, then we could -- and would -- do it
> right.

That's wrong. Linux has supported UDP/RAW pmtu discovery since many many
years.

I have a really old presentation on it (from 2000 or so):

http://halobates.de/net-topics/text33.htm
http://halobates.de/net-topics/text34.htm
http://halobates.de/net-topics/text35.htm
http://halobates.de/net-topics/text36.htm

It's also in the manpages.

However I suspect it's too much work to change a lot of applications
to that, so I suspect the IPV6_MIN_MTU workaround is still needed.

-Andi
-- 
ak@...ux.intel.com -- Speaking for myself only.
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html