IP Fragmentation

Sam Stickland sam_mailinglists at spacething.org
Wed Aug 20 17:07:22 CDT 2008


Iljitsch van Beijnum wrote:
> On 20 aug 2008, at 20:04, Valdis.Kletnieks at 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




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