multimaster - implement multimaster support
As noted in Redmine#1778: So it seems the correct behavior with the multiple masters in a slave zone is:
- On REFRESH, poll all masters and pick highest SOA SERIAL
- On NOTIFY, issue SOA query if the sender is listed as master for given zone OR
- On REFRESH, poll the first one and if it fails, try the rest of the masters on RETRY
What I'm more concerned is, if this feature is of any use at all as it's an easy way to make slave zone inconsistent. And failover is handled with REFRESH/RETRY itself + you can use hidden master model. Any other reasons to implement it?
Related RFCs: