[dns-operations] PMTUD of .org servers

[Florian Weimer]

* Michael Graff:

> Florian Weimer wrote:
>> Is it just me, or do some of the .org servers (notably
>> 199.19.56.1/a0.org.afilias-nst.info) ignore ICMP "fragmentation
>> needed, but DF bit set" message, even though they set the DF bit in
>> the IP header of the response packet?
>
> Is PMTU even defined on UDP?

Yes, it is.  RFC 1191 is somewhat protocol agnostic.

> IMHO, UDP should not have DF set in the common case, and never for
> DNS.  I thought PMTU was more of a TCP thing anyway?

EDNS0 requires PMTUD for DNS, see section 4.5.2 of RFC 2671.  It is
debatable if this requirement is desirable.