[107041] in North American Network Operators' Group
Re: IP Fragmentation
daemon@ATHENA.MIT.EDU (Sam Stickland)
Wed Aug 20 18:07:31 2008
Date: Wed, 20 Aug 2008 23:07:22 +0100
From: Sam Stickland <sam_mailinglists@spacething.org>
To: Iljitsch van Beijnum <iljitsch@muada.com>
In-Reply-To: <010F38F3-2B20-4707-9A29-0950D61C9CC5@muada.com>
Cc: OPS Gurus <nanog@merit.edu>
Errors-To: nanog-bounces@nanog.org
Iljitsch van Beijnum wrote:
> On 20 aug 2008, at 20:04, Valdis.Kletnieks@vt.edu wrote:
>
>> Hypothetically true. Unfortunately, enough places do bozo
>> firewalling and drop
>> the ICMP Frag Needed packets to severely limit the utility of PMTU
>> Discovery.
>
> Yet all OSes have it enabled and there is no fallback to fragmentation
> in PMTUD: if your system doesn't get the ICMP messages, your session
> is dead in the water.
>
Windows Vista/2007 has black hole detection enabled by default. It's not
massively elegant, but it will keep sessions up (falls back to 536 byte
MTU).
http://support.microsoft.com/kb/925280
Sam
