[107068] in North American Network Operators' Group
Re: IP Fragmentation
daemon@ATHENA.MIT.EDU (Fernando Gont)
Mon Aug 25 06:36:10 2008
Date: Mon, 25 Aug 2008 07:27:34 -0300
To: Sam Stickland <sam_mailinglists@spacething.org>,
Iljitsch van Beijnum <iljitsch@muada.com>
From: Fernando Gont <fernando@gont.com.ar>
In-Reply-To: <48AC959A.7030203@spacething.org>
Cc: OPS Gurus <nanog@merit.edu>
Errors-To: nanog-bounces@nanog.org
At 07:07 p.m. 20/08/2008, Sam Stickland wrote:
>>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
IPv4 minimum MTU is 68 bytes, not 536. 536 is the minimum fragment
re-assembly buffer size. Falling back to 536-byte packets does not
guarantee that sessions will be kept up.
Kind regards,
--
Fernando Gont
e-mail: fernando@gont.com.ar || fgont@acm.org
PGP Fingerprint: 7809 84F5 322E 45C7 F1C9 3945 96EE A9EF D076 FFF1
