tcp versus udp

[Barry Margolin]

In article <gtrqte$2ins$1 at sf1.isc.org>,
 Sam Wilson <Sam.Wilson at ed.ac.uk> wrote:

> In article <gtrbsa$296l$1 at sf1.isc.org>, Mark Elkins <mje at posix.co.za> 
> wrote:
> 
> > One place that TCP may make sense - if you are involved in a registry
> > system and the process involves actually checking the information that
> > you are given, including nameservers (do they exist, do they serve that
> > zone - correctly?) - it may make a lot of sense to do TCP Digs for the
> > information (though that should probably be after a failed UDP dig - as
> > a number of people do insist on disallowing Port 53 TCP).
> 
> If the registry is testing for compliant servers then a failed TCP query 
> should flag the server as non-working, as would a failed UDP query.

DNS servers MUST support UDP, and only SHOULD support TCP.  So a failed 
TCP query should not flag the server as non-working.

-- 
Barry Margolin, barmar at alum.mit.edu
Arlington, MA
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