[conspire] DNS? UDP limited to 512 bytes, or ??? ... got EDNS? ...

[Rick Moen]

Quoting Michael Paoli (Michael.Paoli at cal.berkeley.edu):

> Yes, the above still *mostly* holds and it *is* still required for
> properly functioning DNS.  There are, however, a few things that change
> that a bit ... or more properly and precisely - *extend* it.
> 
> UDP limited to only a maximum of 512 bytes in a packet?  DNS can't do
> more than that 512 byte limit in a UDP packet?  That's not necessarily
> always the case ... but it depends upon the particular client and
> server involved - and also the transport between them.  So one can't
> generally expect or rely upon any and all clients and/or servers
> supporting such extensions.  Huh?  Yes.
> EDNS https://en.wikipedia.org/wiki/Extension_mechanisms_for_DNS

So, to be completely accurate, what I should have said to Mark, Edie,
and Joe was 'Specifically, if the [...] answer size exceeds 512 bytes, 
TCP _will often_ [instead of 'must'] be used.'  Conclusion is
nonetheless on the mark that 'It is absolutely necessary that DNS
nameservers be able and willing to respond using TCP-type answers.' 
(Or, as you phrase it, still required for properly functioning DNS.)

I think we've both seen the sort of severe flakiness that occurs when
someone mistakenly firewalls off 53/TCP on a DNS nameserver.  It looks a
lot like what is observed with x7hosting.