IP Fragmentation

Fernando Gont fernando at gont.com.ar
Mon Aug 25 05:27:34 CDT 2008

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).

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 at gont.com.ar || fgont at acm.org
PGP Fingerprint: 7809 84F5 322E 45C7 F1C9 3945 96EE A9EF D076 FFF1

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