How does bind select what master to use?

[Barry Margolin]

In article <mailman.193.1367213994.20661.bind-users at lists.isc.org>,
 Chris Buxton <clists at buxtonfamily.us> wrote:

> 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.

But if all of them have the same serial (and they're all higher than the 
local value, of course), how does it decide which one to transfer from?

-- 
Barry Margolin
Arlington, MA