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: <E1829B60731D1740BB7A0626B4FAF0A649E05EABD5@XCH-NW-01V.nw.nos.boeing.com>
Date:	Tue, 30 Mar 2010 08:58:32 -0700
From:	"Templin, Fred L" <Fred.L.Templin@...ing.com>
To:	Andi Kleen <andi@...stfloor.org>,
	"Edgar E. Iglesias" <edgar.iglesias@...il.com>
CC:	Eric Dumazet <eric.dumazet@...il.com>,
	Rick Jones <rick.jones2@...com>, Glen Turner <gdt@....id.au>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: UDP path MTU discovery



> -----Original Message-----
> From: Andi Kleen [mailto:andi@...stfloor.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@...r.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@...ing.com

> -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