Choose from many name servers that are authorative for the same zone

[Kevin Darcy]

The RTT is a measure of how quickly the nameserver responds to queries. named
keeps track of the RTT for each nameserver and prefers faster ones. What else
do you need to know?

If you wanted to mimic this algorithm manually, you'd have to make multiple
queries to each nameserver in a list, record the RTT of the queries, average
them, and then use the one with the lowest average (if you were doing this
several times over a significant period of time, you'd probably want to use a
"decaying average" so that servers which are temporarily down or slow don't
keep getting penalized long after they recover).


- Kevin

Xindian Long wrote:

> In Paul Labitz' book DNS & BIND, 3rd Edition, chapter 10, Page 244 on the
> topic of "Preferring Name Servers on Certain Networks", there is a
> paragraph like that:
>
> "BIND 8's topology feature is somewhat similiar to sortlist, but it only
> applies to the process of choosing name servers. We described how BIND
> chooses between a number of name servers that are authorative for the same
> zone earlier in the book--by selecting the name server with the lowest
> roundtrip time. But we lied a little. BIND 8 actually places remote
> nameservers in 64 millisecond bands when comparing RRT. The first band is
> actually only 32 millisecond wide,... The next extends from 33 millisecond
> to 96 milliseconds, and so on. ...
>
> The idea is to favor name servers in lower bands but to treat servers in
> the same band as equivalent. If the name server compares two remote
> server' RTTs and one is in a lower band, the name server will choose to
> send the query to the name server in the lower band......."
>
> In the following section the book starts to talk how to use "Topology" to
> choose from many name servers within the same band. However, I cannot find
> the section about       "BIND chooses between ... by selecting the name
> server with the lowest roundtrip time" .
>
> Could anyone tell me where I can find the information about this feature ?
> i.e. how to choose a name server with the lowest RRT ?
> Thanks a lot.
>
> Xindian