replicating dynamicly updated servers..

Chris Buxton cbuxton at
Wed Sep 6 13:41:02 UTC 2006

On Sep 6, 2006, at 6:14 AM, Gregory Machin wrote:

> On 9/5/06, Kevin Darcy <kcd at> wrote:
>> Gregory Machin wrote:
>>> Hi
>>> I have a master dns server (bind 9) that has 2 zones that clients  
>>> update
>>> dynamicly... Bind doesn't allow for slave serve to be updated for a
>> dynamic
>>> zone ....
>>> How can I work around this .. as I need a backup server so if the  
>>> primay
>>> master is down the clients can still resolve ...
>> What you're describing -- having multiple servers that can accept
>> Dynamic Updates for the same zone -- is usually called "multi-master"
>> and vanilla BIND does not support it at this time. The problem, as I
>> understand it, is what to do about conflicting updates, e.g. client A
>> adds record X but client B deletes X. Do you go by timestamp, or some
>> other attribute of the respective updates? The only way I'm aware of
>> that multi-master has been implemented with at least partial  
>> success is
>> when there is a back-end database -- e.g. LDAP for Active
>> Directory/Microsoft DNS, or a regular DBMS such as Oracle or  
>> Sybase for
>> Lucent's QIP product (using a modified version of BIND) -- which  
>> acts as
>> a kind of "central arbitrator" and will prevent conflicting  
>> updates from
>> getting out of hand.
> A slave server does not allow for updates directly from the client ...
> Yes a "multi-master" is what I'm looking for ...
> But from what I here the backend database engens are not stable  
> with bind
> and have limited functionality .. ?
> Any sugetions ?

As Kevin said, you need multiple master servers. Normal BIND doesn't  
support this, but there are several solutions that do:

- Active Directory is built for this. If you use an AD-integrated  
zone with MS DNS, changes can be sent to any DC.
- Infoblox uses a (heavily) modified version of BIND to allow this,  
similar to MS DNS in an AD environment.

There may be other solutions (not including QIP, which Kevin already  
mentioned), but I don't know of any that involve the vanilla version  
of BIND. It's not a simple thing to implement.

With the standard version of BIND, you can configure the slaves to  
forward updates to the master server if they are received from  
clients. But if the master is down, you're still out of luck.

Chris Buxton
Men & Mice
Take control of your network

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