Subject: RE: Non-incrementing SOA (Re: RFC2136 question)

From: "James Gilroy (Exchange)" <[email-masked]>
Date: Wed, 17 Nov 1999 13:49:26 -0800

For the record:  the behavior Harald saw in the Microsoft DNS server was a
lookup to WINS.

This was a feature I put into the NT4 DNS server, to allow customers to give
"DNS-visibility" to windows boxes that were DHCP configured and hence
(pre-2136) would not have their mappings in a zone file.

For those who care the basic paradigm is
	-- windows clients register their names with WINS (netBIOS IP name
server)
	-- DNS zone can be configured to lookup unknown name in WINS
server(s)
	-- if DNS server gets response from WINS, it responds to DNS query
(and caches A record)
	-- however A record is not XFRed because it is dynamic data not
guaranteed to be valid for more than a brief interval
	(secondaries who want to give out the same data can be configured
for WINS lookup like the primary)

This was basically a solution to ease transition of customers from netBIOS
(flat) to DNS naming.  At the time I wrote it, DNS dynamic update didn't
exist.  With NT5, the DNS server supports dynamic update and the clients
attempt -- by default -- to register themselves.

	jim

From: Harald Tveit Alvestrand [mailto:[email-masked]]
Sent: Wednesday, November 17, 1999 7:04 AM
To: Robert Elz; [email-masked]
Cc: namedroppers
Subject: Non-incrementing SOA (Re: RFC2136 question)

At 18:41 11.11.99 +1100, Robert Elz wrote:

>   | There remains one thing I'm not clear on. Is it a no-no for a DNS 
> server to
>   | present different data at different times with the same SOA serial 
> number ?
>
>Yes - while I am not sure right now that anything actually depends upon
>that behaviour (I don't know of anyone doing SOA checks and refreshing
>TTLs for example, though it could be done).
>
>   | e.g. if I did "dig @slave zone AXFR" at two different times and I 
> would get
>   | different data, but the same SOA serial number.
>
>That would certainly be broken (for the internet environment of course - in
a
>private world, if you can cope, cope).   2136 is quite clear that the
serial
>number must be incremented whenever the zone data is changed, and the
serial
>number is exposed.   That wasn't changing anything in 1034, just 
>emphasising it.

I've seen a (Microsoft) nameserver present changing data (dynamically 
inserted based on DHCP action) while not incrementing the serial number.
So I could ask for the A record of alden.maxware.no at 2 different times 
and get back 2 different answers, yet the SOA serial number was the same.

However, that one did the additional twist of not including those data in 
the AXFR of the zone at all, which means that a secondary wouldn't see the 
data that was changing - perhaps it didn't consider this to be zone data?

I personally think this is bizarre, but others may think otherwise...

(No, I don't have the serial number, and haven't checked it for the last 6 
months. I could check again if someone cares.)

                          Harald

--
Harald Tveit Alvestrand, Maxware, Norway
[email-masked]

---

From: "Stuart Kwan (Exchange)" <[email-masked]>
Date: Thu, 18 Nov 1999 13:33:08 -0800

For more information on the WINS lookup functionality described below, see
http://www.ietf.org/internet-drafts/draft-levone-dns-wins-lookup-00.txt.

Cheers,
- Stuart