Resolver behaviour with rrset

[Sebastian Castro Avila]

On Wed, 26 May 2004 00:42:00 +0100, Jim Reid <jim at rfc1035.com> wrote:

>     Sebastian> How does it work if a server became unreachable?
>
> That server is considered to have an infinite round trip time. [For
> some definition of "infinite".] So the dead server won't get queried
> much after it became unreachable, all other things being equal. However
> the resolving name server will periodically "forget" the dead server
> has an infinite RTT and query it once more. Any response or
> non-response is then used to update the server's idea of which name
> server is closest for a given domain. This means a name server's
> resolver is continually keeping track of the RTTs to the name servers
> it queries and adjusting those RTTs in light of what is currently
> going on.
>

So, I should think that this resolver will choose a server based on a  
"weighted list", where this weight is based on response time. The server  
with better response time will be prefered, but it won't be the "only one"  
used.


>     Sebastian> How often the resolver updates the response time for
>     Sebastian> the whole list of known servers?
>
> It depends.
>
>     Sebastian> Where can I get more information about this "feature"?
>
> Section 7.2 of RFC1035 explains some of the factors that can be taken
> into consideration. You can also read the source code to see what BIND
> does. To a large extent, this feature is an opaque implementation
> detail. Frankly, most people don't (need to) care about this. They
> just trust that their name servers generally favour the fastest
> responding name server for some zone and will do the Right Thing
> whenever any dead servers come back to life or a nearby server goes
> away.
>
> Have you a specific reason for asking about this or are you just curious?

Both.
I'm looking for some master thesis, and I'm exploring the posibility of  
making a "model" or simulation to choose the right place and the right  
capacity for a set of nameservers for a domain.

Moreover, I'm studying the benefits of placing F root server replicas  
around the world. In particular, we are considering have a replica here in  
Chile, so I'm looking some good reasons to have one.

Some reasons are obvious: Better Internet infraestructure.
But I'd like to figure out if networks topologically close to the replica  
will choose it ALWAYS or MOST OF THE TIME, to send valid queries to it.  
The Round Robin behave in the same way or became a weighted Round Robin,  
where closest servers are used more frequently?


>
> ISTR there was a discussion in bind-users or bind-workers some years
> ago about RTT maintenance. So it might be worth checking the list
> archives.

I'll google a bit and check them out for more information.

Thanks for your answer.
-- 
Sebastian E. Castro Avila             sebastian at nic.cl
Administrador de DNS, NIC Chile
Fono: (2) 9407705                  Fax  : (2) 9407701