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From: "Templin, Fred L" <Fred.L.Templin@boeing.com>
To: Andi Kleen <andi@firstfloor.org>,
	"Edgar E. Iglesias" <edgar.iglesias@gmail.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>,
	Rick Jones <rick.jones2@hp.com>, Glen Turner <gdt@gdt.id.au>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>
Subject: RE: UDP path MTU discovery
Date: Tue, 30 Mar 2010 08:58:32 -0700	[thread overview]
Message-ID: <E1829B60731D1740BB7A0626B4FAF0A649E05EABD5@XCH-NW-01V.nw.nos.boeing.com> (raw)
In-Reply-To: <20100330061952.GO20695@one.firstfloor.org>



> -----Original Message-----
> From: Andi Kleen [mailto:andi@firstfloor.org]
> Sent: Monday, March 29, 2010 11:20 PM
> To: Edgar E. Iglesias
> Cc: Andi Kleen; Templin, Fred L; Eric Dumazet; Rick Jones; Glen Turner; netdev@vger.kernel.org
> Subject: Re: UDP path MTU discovery
> 
> > If you don't want to hassle with all of that, the app can stick to
> > 1280 (or I guess for the extreme/lazy cases turn on fragmentation)..
> 
> See the early mails in this thread. This is about apps who can't
> limit themselves to 1280, but still don't want full blown PMTU.
> [They probably should, but it can be a lot of work]

Right. Some apps may need to send isolated packets that
are larger than the path MTU without invoking path MTU
discovery.
 
> The MTU would allow to force fragmentation on the sending host
> as a workaround similar to IPv4.

Right again. Unlike IPv4, however, IPv6 does not allow
in-the-network fragmentation. So when in doubt, apps
that need to send isolated packets that may violate the
path MTU should really perform host-based fragmentation
with a maximum fragment size of 1280. Isn't there a
socket option "IPV6_USE_MIN_MTU" that apps can use to
force fragmentation on large packets (RFC3542)?

Caveat - the app may have no way of knowing whether
the destination is capable of reassembling fragmented
packets larger than 1500...

Fred
fred.l.templin@boeing.com

> -Andi
> --
> ak@linux.intel.com -- Speaking for myself only.

  parent reply	other threads:[~2010-03-30 16:32 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2010-03-26  0:02 UDP path MTU discovery Glen Turner
2010-03-26  0:53 ` Rick Jones
2010-03-26  3:26   ` David Miller
2010-03-26 17:48     ` Rick Jones
2010-03-31 23:42     ` Glen Turner
2010-03-31 23:51       ` Hagen Paul Pfeifer
2010-04-01  0:06         ` Rick Jones
2010-03-26  3:24 ` David Miller
2010-03-28  8:41   ` Andi Kleen
2010-03-31 23:57     ` Glen Turner
2010-04-01  0:57       ` Andi Kleen
2010-03-28  8:50 ` Andi Kleen
2010-03-29 17:01   ` Rick Jones
2010-03-29 20:14     ` Andi Kleen
2010-03-29 20:25       ` Rick Jones
2010-03-29 20:50       ` Edgar E. Iglesias
2010-03-29 21:01         ` Rick Jones
2010-03-29 21:29           ` Eric Dumazet
2010-03-29 23:38             ` Templin, Fred L
2010-03-30  5:20               ` Andi Kleen
2010-03-30  6:06                 ` Eric Dumazet
2010-03-30  6:16                   ` Andi Kleen
2010-03-30  6:17                   ` UDP path MTU discovery II Andi Kleen
2010-03-30  6:16                 ` UDP path MTU discovery Edgar E. Iglesias
2010-03-30  6:19                   ` Andi Kleen
2010-03-30  8:20                     ` Edgar E. Iglesias
2010-03-30 14:12                       ` Andi Kleen
2010-03-30 22:04                         ` Edgar E. Iglesias
2010-03-30 15:58                     ` Templin, Fred L [this message]
2010-03-30 16:06                       ` Andi Kleen
2010-03-31 23:43     ` Glen Turner
2010-04-01  0:55       ` Andi Kleen
2010-04-02  5:41         ` Glen Turner
2010-04-04 10:25           ` Andi Kleen

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