How does bind select what master to use?

[Chris Buxton]

On Apr 27, 2013, at 5:52 AM, Matus UHLAR - fantomas wrote:

> On 27.04.13 01:03, Kevin Morgan wrote:
>> Does it use an algorithm to determine the best server to use or does
>> it try the masters in the order they are listed? I am wondering if
>> listing the masters in a different order can optimize the performance
>> of bind.
> 
> AFAIK:
> BIND keeps track of servers accessible and their RTT. It tends to prefer
> theone with shoertet RTT but ocasionally re-tries (RTT can change over
> time. If notice comes, BIND tends to prefer server that has sent it.

If you're talking masters, as in the BIND server is a slave refreshing from its masters, then I don't believe that's correct. I believe it compares the serial numbers retrieved from each and prefers the one with the highest value.

If you're talking about forwarding to forwarders, then yes, RTT is used. If you're talking about recursion, then yes, RTT is used.

Chris Buxton