[RSSAC Caucus] [Ext] TCP and TC (was Updating the RSSAC FAQ)

[Mukund Sivaraman]

On Mon, May 04, 2020 at 09:01:47AM -0700, Fred Baker wrote:
> Sending again using the right email address.
> 
> > On May 4, 2020, at 9:01 AM, Fred Baker <fredbakersba at gmail.com> wrote:
> > 
> > Stepping aside a bit from the question of the FAQ... Yes, this is a change of subject, which is why I changed the subject line.
> > 
> > Does this become a requirement for resolvers using the RSS? RFCs 1034/1035 only hint at it (they define the bit without defining its use case). If, however, I look at RFC 2181, it says
> > 
> >   Where TC is set, the partial RRSet that would not completely fit may
> >   be left in the response.  When a DNS client receives a reply with TC
> >   set, it should ignore that response, and query again, using a
> >   mechanism, such as a TCP connection, that will permit larger replies.

There was some previous treatment in RFC 1123 (section 6.1.3.2):

> DNS resolvers and recursive servers MUST support UDP, and
> SHOULD support TCP, for sending (non-zone-transfer) queries.
> Specifically, a DNS resolver or server that is sending a
> non-zone-transfer query MUST send a UDP query first.  If the
> Answer section of the response is truncated and if the
> requester supports TCP, it SHOULD try the query again using
> TCP.

> DNS servers MUST be able to service UDP queries and SHOULD
> be able to service TCP queries.  A name server MAY limit the
> resources it devotes to TCP queries, but it SHOULD NOT
> refuse to service a TCP query just because it would have
> succeeded with UDP.

> Truncated responses MUST NOT be saved (cached) and later
> used in such a way that the fact that they are truncated is
> lost.

As Ray has said, RFC 7766 made TCP a requirement.

		Mukund