Authoritative Redundancy

Kevin Darcy kcd at
Thu May 20 16:59:23 UTC 2010

If your primary master goes down, and you want to ensure that all of 
your slaves get the *latest*available*version* of the zone, and serves 
it until the master comes back up, then you would "cross-connect" all of 
your slaves so that eventually they'll all sync up to that version.

*HOWEVER*, because of protocol limitations, this will essentially break 
zone expiration. If you delete a zone on the master, in other words, and 
forget to delete the definition on 2 or more slaves, then they'll keep 
"refreshing" from each other indefinitely, since the refresh timer gets 
reset even if nothing changes in the zone. The zone is "immortal" on 
those slaves, and manual intervention will be necessary to get rid of it.

A protocol fix for this was floated to the IETF Working Group, but not 
enough interest was generated to make any kind of change.

If your configuration-control system reliably deletes all slave-zone 
definitions, then maybe this is a non-issue for you.

                                         - Kevin

On 5/20/2010 12:08 AM, Baird, Josh wrote:
> Would there be any benefit in assigning them as additional master's 
> for all of my zones (in addition to DNS01), or would this just 
> complicate the entire environment?
> Thanks
> In article <mailman.1534.1274300384.21153.bind-users at>,
>  "Baird, Josh" <jbaird at> wrote:
> > Hi,
> >
> > I currently have three authoritative servers in the RRset for my
> > internal zones:
> >
> >         NS
> >         NS
> >         NS
> >
> > DNS01 is the sole master for my internal zones.  I have a number of
> > resolving DNS servers throughout my environment that contain slave
> > definitions for my internal zones to override recursion.  These slave
> > definitions use DNS01 as their master (only DNS01, not DNS02/03).
> >
> > zone "" IN {
> >         type slave;
> >         masters { DNS01's_IP_ADDRESS; };
> >         file "hosts/slaves/";
> > };
> >
> > DNS02 and DNS03 also contain slave zones for all of my internal zones.
> > Their master is also DNS01.
> >
> > My question is.. am I gaining anything by having DNS02/DNS03?  With
> > DNS01 being my sole master, it doesn't seem like DNS02/DNS03 are
> > providing any additional benefit.  How could I make a better use of
> > DNS02/DNS03?  Recursion is disabled on them, and no clients directly
> > query them; they query the numerous resolving DNS servers throughout the
> > environment.
> I think you can safely get rid of them.  With all your internal
> resolvers running as stealth slaves for your zones, you don't need
> published slaves.  NS records are only used by recursive servers.
> --
> Barry Margolin, barmar at
> Arlington, MA
> *** PLEASE don't copy me on replies, I'll read them in the group ***
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