Changing the Resolvers Timeout

Changing the Resolver s Timeout

9.6.1 Problem

You want to change a resolver's timeout.

9.6.2 Solution

With a resolver based on BIND 8.2 or later code, use the options timeout directive in resolv.conf. The directive's argument is a timeout in seconds, separated from the keyword timeout with a colon. For example, to set the initial timeout to two seconds, you could add this directive to resolv.conf:

options timeout:2

The maximum value is 30 seconds; the minimum is 1 second.

The default timeout for the first round of queries is five seconds per name server. After each round of queries to the name servers listed in resolv.conf, the resolver doubles the initial timeout. BIND 8.2 and previous resolvers send a total of four rounds of queries; BIND 8.2.1 and later resolvers send two.

There is no way to modify the timeouts in a Windows resolver. However, the default timeouts are fairly short in newer Windows resolvers (one second for the first query in Windows 2000, for example), so adjusting them may not be necessary.

9.6.3 Discussion

If you're using a BIND 8.2 or later resolver, you may also find it useful to change the number of rounds of queries the resolver sends with options attempts. options attempts takes an integer number of attempts as an argument, after a colon. For example:

options attempts:1

Again, the default value is four up to BIND 8.2, and two thereafter. The maximum value for the option is five.

To specify multiple options, use a single options directive, like so:

options timeout:2 attempts:4

If you or your users are experiencing lots of timeouts, however, consider taking a close look at your name servers before monkeying with the resolver timeout. A correctly configured, reasonably loaded name server should be able to respond to nearly any query in less five seconds, assuming that the name servers authoritative for the zone that contains the answer are reachable and themselves correctly configured.

9.6.4 See Also

"The options Directive" in Chapter 6 of DNS and BIND; "Name Servers to Query" in Chapter 6 of DNS on Windows 2000.