forwarding algorithm and timeouts

[Bob Vance]

Thanks, Kevin.

>is actually assuming the role of a "resolver",
>basically a stub-resolver-with-caching.

Well, surely it's not trying the list more than once?  -- like the stub
resolver algorithm described in 'DNS and BIND' and in contradiction to
the documentation where it says that the "forwarders" are tried each
only once.



> don't recall offhand if there
>are any specific parameters in the RFCs regarding resolver timeouts...

So, still, I'm wondering what that timeout is and the rationale for its
value, whatever it may be.


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-----Original Message-----
From: bind-users-bounce at isc.org [mailto:bind-users-bounce at isc.org]On
Behalf Of Kevin Darcy
Sent: Monday, March 26, 2001 5:00 PM
To: bind-users at isc.org
Subject: Re: forwarding algorithm and timeouts



Bob Vance wrote:

> What exactly is the forwarding algorithm, assuming that "forward only"
> is set.
> Or where can I read about it (besides the source code :) ?
>
> I checked the ARM, but only found this brief statement:
>
>    "they are queried in turn until the list is exhausted or an answer
>     is found.
>    "
>
> Hmmm. I just looked in 'DNS and BIND, 2nd' and it says:
>
>    "each forwarder is contacted only once, and it waits a short time
>     for the forwarder to respond.
>    "

Actually, as of BIND 8.2.3, the forwarders are supposedly tried
according
to historical RTT, not necessarily sequentially...

> OK.  What is the timeout used before going to the next one in the
list?
> I would assume that it would have to be ~5 since we know that the stub
> resolvers wait this long on their initial try.  Otherwise, we could
get
> several outstanding request from resolvers before the first forwarder
> try times out.
>
> Do all resolvers follow the algorithm described in 'DNS and BIND' ?
> I.e., do WinX or MAC clients also try their list initially with 5
> seconds, then re-do the list with 10 seconds, etc.?
> Is this algorithm a requirement described in an RFC?

In RFC terms, a nameserver doing "forward only" isn't really acting as a
"nameserver" _per_se_, but is actually assuming the role of a
"resolver",
basically a stub-resolver-with-caching. I don't recall offhand if there
are any specific parameters in the RFCs regarding resolver timeouts...


- Kevin