Subject: Finding server for Dynamic Update?

From: Stuart Cheshire <[email-masked]>
Date: Mon, 19 May 2003 17:34:30 -0700

Question:

To do a DNS Update, you need to know the DNS server to which the Update 
packet should be sent.

My intended algorithm would simply be to find the parent zone name of the 
name being updated (e.g. from the SOA record), and then look up the NS 
records for that zone name, and then send the Update to one of those DNS 
servers.

Unfortunately, some sites have Update enabled on only *one* server, and 
that server is *not* listed in the NS records.

One solution would be simply to make the end user manually configure the 
name of the Update server, but I'd rather not put that additional 
configuration burden on the end user.

The established DNS mechanism for locating an instance of some service
is SRV records. Perhaps this offers a solution for discovering
a domain's update servers? The problem here is that the SRV name 
"_domain._udp.apple.com." doesn't make any distinction between the two
different services "DNS Update" and "DNS Query". Both Update and Query
use DNS protocol on port 53, but semantically they are quite different
services.

The solution I have in mind is to use some other name, such as
"_domainupdate._udp.apple.com." Even though the port number is usually
still 53, this SRV record would denote a semantically different service.
When a client looks up this SRV record, it is conveying that it is
seeking the entity that handles DNS updates for that domain, not
just any old DNS server that only handles queries.

An alternative naming, which reflects the status of "update" servers as
a subset of all DNS servers, might be "_update._domain._udp.apple.com."
This naming is logical, but it doesn't follow the strict
"_application-protocol._transport-protocol." structure recommended in
RFC 2782. Of course, the DNS server doesn't care whether the name
follows the RFC 2782 convention -- the question is whether human
operators think it is important.

It really doesn't matter what name we pick, as long as we can pick one 
name and agree on it.

Comments?

Stuart Cheshire <[email-masked]>
 * Wizard Without Portfolio, Apple Computer, Inc.
 * www.stuartcheshire.org

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