On 2014-05-07 15:06, Lawrence K. Chen, P.Eng. wrote:
OTOH, the idea of multi-master is intriguing.....the only down side I see, is 
hat I have one really powerful server for my current master....(Sun Fire 
X4170)....and my other servers are weak leftovers....just passed EOL last year. 
 And, have all the servers doing full DNSSEC signing could be interesting.

It also raises the question of how does the outside world cope with all the 
servers having identical zones...signed on slightly different times, etc. 
(especially since I'm using unix timestamp for zone serial....avoids issues of 
multiple admins incrementing serial without noticing others and/or collisions 
with DNSSEC's incrementing of serials.)

I wouldn't expect any real issues here, Windows DNS has done multimaster DNS since Windows 2000. In the case of Windows, dynamic updates (via client or GUI) can be done at any location, the serial numbers are incremented automatically, but the zones and servers may vary from each other for a brief period of time.

So for example, DC1 and DC2 may start with serial 100, DC1 will receive 2 changes and be up to 102, DC2 will give 5 different changes and be up to 105. When Active Directory synchronization happens outside of DNS, the two sides merge changes together, and set the serial to the higher of the two plus one, so the serial would be 106. To the outside world, records can appear/disappear for a brief period while the servers drift out of sync, similar to what could happen in a BIND configuration without notifies as resolvers hit the two DNS servers round-robin.

The only thing that causes issues is if you use DNS to create a non-Active Directory slave. BIND will throw errors because it will see serial 100, 101, 102, then get a notify from the second server about 101. However, the slave will still sync up once the AD servers sync to 106. The fix here is to configure BIND to only slave off of one master or the other, not both.

While there might be other factors involved in turning BIND into a true multi-master solution, I wouldn't expect zones drifting out of sync or having minor differences to be a big factor since it happens in the wild already.

--
Dave Warren
http://www.hireahit.com/
http://ca.linkedin.com/in/davejwarren


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