Forwarders and performance

Cricket Liu cricket at acmebw.com
Fri Oct 22 17:07:07 UTC 1999


> I'm considering forwarders as they relate to performance.  Having read
> through Albitz & Liu (3rd Ed.), I am left with this understanding of
> forwarders as their use relates to nameserver performance:
>
> 1. In the short term (soon after [re]starting named) I will get better
> performance in name resolution by having these lines in the options {}
> section of my config file:
>
>         forward first;
>         forwarders { 24.4.162.33; 24.4.162.34; };
>
> The performance win is that my ISP's nameservers (the addresses above)
> may already have cached the information I will need.  If the info is not
> already cached, I will fall back to resolving the name in question via
> the root nameservers.

No.  Your name server will fall back to doing iterative name resolution
(starting with the root name servers, if necessary) only if those two name
servers don't respond in about 60 seconds.  Since the forwarders are
receiving recursive queries, they'll assume the burden of resolving the
domain
names, whether or not the name is cached.

> Note that my ISP is @Home, which has a large subscriber base.  This make
> it pretty likely that the IP address I want is in their nameserver's
> cache.  On the other hand, I still have to gain this information by a
> call to a server outside my own network.
>
> 2. There is a long term (named has been running for a while) gain to
> *not* having these to options defined as this forces all name resolution
> to be done via the root nameservers.  My local nameserver will gain
> general resolution info in the course of resolving a given specific
> name.  This general info will speed later resolutions by allowing me to
> skip calls to the root nameservers and possible to top-level domain name
> servers as well.  The win here is the reduced need to "leave" my own
> network in the course of a name lookup.
>
> Does this about sum it up or have I overlooked something?

That's about right.

cricket

Acme Byte & Wire
cricket at acmebw.com
www.acmebw.com

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