IP tunnel MTU

Chris Woodfield rekoil at semihuman.com
Mon Oct 29 23:40:22 UTC 2012


True, but it could be used as an alternative PMTUD algorithm - raise the segment size and wait for the "I got this as fragments" option to show up...

Of course, this only works for IPv4. IPv6 users are SOL if something in the middle is dropping ICMPv6.

-C

On Oct 29, 2012, at 4:02 PM, Templin, Fred L wrote:

> Hi Bill,
> 
>> Maybe something as simple as clearing the don't fragment flag and
>> adding a TCP option to report receipt of a fragmented packet along
>> with the fragment sizes back to the sender so he can adjust his mss to
>> avoid fragmentation.
> 
> That is in fact what SEAL is doing, but there is no guarantee
> that the size of the largest fragment is going to be an accurate
> reflection of the true path MTU. RFC1812 made sure of that when
> it more or less gave IPv4 routers permission to fragment packets
> pretty much any way they want.
> 
> Thanks - Fred
> fred.l.templin at boeing.com
> 




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