RESOLVERTIMEOUT statement

Use the RESOLVERTIMEOUT statement to specify the amount of time the resolver waits for a response while trying to communicate with a name server when using UDP. See RESOLVEVIA statement.

Parameters

system_name:

The name of the system to which this statement applies. See system_name considerations for a complete description of this parameter.

Requirement: The colon is required.

time_out_value

The time the resolver waits until a response is received from a name server. The time can be specified in whole seconds, milliseconds, or a combination of both. For example, the RESOLVERTIMEOUT value can be 11, .110, or 1.100.

A time_out_value value that is less than 10 milliseconds is set to 10 milliseconds (0.010). For example, RESOLVERTIMEOUT 0.005 is processed as RESOLVERTIMEOUT 0.010.

A time_out_value value of 0 is equivalent to RESOLVERTIMEOUT 1.

Specifying more than three decimal positions is considered a parse error and is ignored. For example, RESOLVERTIMEOUT 0.0100 is a parse error and is not processed.

The default timeout value is 5 seconds; the maximum timeout value is 2147483.647.

Steps for modifying

You can refresh this statement using the MODIFY command. For more information about parameters used with the MODIFY command, see z/OS Communications Server: IP System Administrator's Commands.

Usage notes

The resolver uses the RESOLVERTIMEOUT value when it is waiting for a response to a resolver DNS polling query. The resolver sends resolver DNS polling queries to a name server when AUTOQUIESCE is specified on the UNRESPONSIVETHRESHOLD resolver setup statement and the name server is considered unresponsive. If the RESOLVERTIMEOUT value is changed using the MODIFY RESOLVER,REFRESH command, the new time value applies only to resolver DNS polling queries that are sent by the resolver after the MODIFY command is processed. See UNRESPONSIVETHRESHOLD statement for more information about when the resolver considers a name server to be unresponsive.

Guideline: If you use the autonomic quiescing of unresponsive name servers function, you should specify a timeout value of 5 seconds or less.

The SMTP server and the BIND 9 DNS utilities provide their own resolver that supports RESOLVERTIMEOUT values in seconds. If a time_out_value of less than 1 second is specified, these resolvers use a one second timeout. For a time_out_value of seconds.milliseconds, the specified seconds are used as the timeout value.

Be careful when assigning a short time_out_value. A number too small can result in timeouts occurring even when the network or name server is available, but due to high usage volume, it cannot respond quickly. Review the RESOLVERUDPRETRIES statement to see if a higher value should be specified for the maximum number of tries the resolver can make when using a name server.

Tip: Timeout conditions can cause the z/OS® resolver to mistakenly act as though the name server does not support Extension Mechanism for DNS (EDNS0). This can prevent the z/OS resolver from using EDNS0 when it could otherwise be used; this behavior can adversely affect performance. For more information about ENDS0 processing, see z/OS Communications Server: IP Configuration Guide.

Guideline: The resolver uses the API services of z/OS Unix System Services to manage the time_out_value value. z/OS Unix System Services uses the following criteria for timer resolution, if the time_out_value is one of the following values:

• Less than 1 second, the timer resolution is set to the next microsecond.
• Greater than 1 second, the timer resolution is set to the next second.