The resolver setup file is an optional file (either an MVS™ data set or a z/OS® UNIX file) that contains resolver configuration statements that you can use to customize resolver functions.
If the resolver setup file is an MVS data set, the file must have the following characteristics:
If the resolver setup file is a z/OS UNIX file, the file can be located in any directory. The maximum line length that is supported is 256 characters. If a line is longer than 256 characters, then the line is truncated to 256 characters before it is processed.
If you do not use a resolver setup file, the resolver uses the applicable native MVS or z/OS UNIX search order without any additional information and performs the following functions using the default settings:
The following statements are supported by the resolver setup file:
Enables system-wide caching of DNS queries that have been resolved. System-wide caching is enabled by default, but you can explicitly enable it using this statement. For more information about caching, see Resolver caching.
Defines the amount of storage that can be allocated by the resolver to manage cached records.
Indicates that the same search order for local host files is used for both IPv4 and IPv6 name queries.
Identifies the default local host file.
Identifies a default TCPIP.DATA file. The file that is specified by the DEFAULTTCPIPDATA statement becomes the last file that is searched by the resolver for resolver configuration information. If you do not specify the DEFAULTTCPIPDATA statement, the default file is TCPIP.TCPIP.DATA. For more information, see The resolver and the global TCPIP.DATA file.
Identifies a local host file that contains hard-coded IP addresses and host names that can be used globally.
Identifies the file that is the first file that is searched by the resolver for resolver configuration information. Parameters that you specify in the file that is identified by the GLOBALTCPIPDATA statement become the global settings for the entire MVS image and for all TCP/IP stacks. For more information, see The resolver and the global TCPIP.DATA file.
Defines the amount of time that the resolver can use resource information that it receives from a name server.
Disables system-wide caching of DNS response data. If you do not specify this statement, system-wide caching is enabled by default.
Indicates that a different search order for local host files is used for IPv4 and IPv6 name queries.
Identifies the threshold value that determines when the resolver declares a DNS name server to be unresponsive. If the percentage of query failures to a name server during a fixed interval is greater than or equal to this threshold value, the resolver considers the name server to be unresponsive. The resolver might stop sending DNS queries that are generated by an application to unresponsive name servers, depending on the values that are coded on this statement. For more information, see Monitoring the responsiveness of Domain Name System name servers.
For more information about resolver setup statements, see z/OS Communications Server: IP Configuration Reference.