[dns-operations] PMTUD of .org servers

[Florian Weimer]

* Rick Jones:

> However, as this can sometimes call for successive resends, IIRC many
> (most?) stacks may disable setting DF on IPv4 datagrams carrying UDP
> datagrams.

Linux sets the DF bit on outgoing UDP packets by default.  It would be
curious if this was a Linux peculiarity (it wouldn't be the first, of
course).  For Linux, PMTUD is very cheap to implement because the
stack cannot send an IP packet without a route cache entry for the
destination /32 (which causes other issues, of course).