[dns-operations] UDP fragmentation while not needed/wanted DS www.veilingzaalmelase.be

Paul Vixie paul at redbarn.org
Thu Mar 25 22:36:22 UTC 2021


On Wed, Mar 24, 2021 at 11:25:48PM +0100, Florian Weimer wrote:
> > ...
> 
> Proactive fragmentation irrespective of path MTU is required for
> stateless IPv6 UDP services.  Unlike IPv4, the network does not
> fragment packets.  So a UDP service has to conservatively fragment
> around 1200 or so bytes (to account for tunnel overhead).  ...

1280 subtracts several hundred bytes from 1500 to allow for tunnel
overhead. 1232 subtracts dozens more to allow for IP and UDP headers
and options.

please, nobody, subtract even more. if everyone subtracts a fudge
factor, forever, we'll eventually run out of payload space, or worse,
go negative.

-- 
Paul Vixie


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