does serial number ever affect cache timeout?

[Mark.Andrews at nominum.com]

> We all know that the serial number in the SOA controls master-to-slave
> synchronization. If the serial number isn't updated when an entry is
> added to a zone, the slave won't get the entry, because it will see
> that its serial number is the same as the master's for that zone, and
> do nothing.
> 
> But in any case does the serial number affect other nameservers out
> on the Internet - in particular, how long they cache a record? I am
> convinced that it is only the TTL (either the $TTL in newer BINDs,
> or else the zone TTL, or else a record-specific TTL) that controls
> how long each record stays in cache on other servers. Unless, that is,
> someone has warped the nameserver somehow to disregard the TTL from
> the authoritative server and insert its own (people always say that
> AOL does this).
> 
> I'm having an argument about this right now, and wanted to make sure
> my bases are covered. It relates to a situation where the authoritative
> servers were changed for a zone, and the new servers had a lower serial
> number set for the zone than the old servers. Some hosts at various
> places are still seeing the old record, and my contention is that it's
> because the TTL at the old servers was set for several days. The other
> party contends that the serial number is the problem, and that until
> the serial number is updated, some hosts out on the Internet will 
> continue to see the old record forever. Both of the new authoritative
> servers, however, are synchronized just fine, and the TTL set to 10800.
> 
> Am I missing something?
> 
> Thanks,
> Rob
> 
> 

	As long as all the servers for the zone (new and old) are
	serving the same zone contents things will be ok.

	If the new and old servers are serving different versions
	of the zone the clients can get locked to a particular set
	of servers.  This is true even if the delgation changes as
	the clients never see the delegation change.  They keep
	getting fresh copies of the NS RRset from the old servers
	so they never need to go to the parent servers.

	Mark
--
Mark Andrews, Nominum Inc.
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: Mark.Andrews at nominum.com