MODIFY command: Resolver address space

You can refresh the resolver address space from the operator console using the MODIFY command. Issue the REFRESH command to refresh the resolver address space and the DISPLAY command to display the current values of the resolver setup statements. Issue the FLUSH command to delete the contents of the resolver cache. You can also reset the current z/OS® knowledge of name server capabilities by issuing the REFRESH command.

For a description of the resolver setup statements, see Resolver setup statements in z/OS Communications Server: IP Configuration Reference.

Parameters

procname

The member name of the cataloged procedure used to start the resolver.

You can use the Display OMVS,O command to determine the procname value. The output displayed includes a line as follows:

RESOLVER PROC   = DEFAULT

If DEFAULT is displayed, then the procname value is RESOLVER. Any other value must be used as the procname.

Display

Displays the current resolver setup statement values. If the autonomic quiescing of unresponsive name server function is active, the resolver also displays the status of the name servers specified on NSINTERADDR statements in the global TCPIP.DATA file.

FLUSH

Deletes the contents of the resolver cache.

ALL

All resolver cache entries are deleted.

REFRESH

Causes applications to have their TCPIP.DATA information updated on their next resolver request after the refresh occurs, including local host tables (for example, etc/hosts, etc/ipnodes, HOSTS.SITEINFO, HOSTS.ADDRINFO, or ETC.IPNODES information). For more information about what TCPIP.DATA information can be updated, see Dynamically changing TCPIP.DATA statements in z/OS Communications Server: IP Configuration Reference.

Resets information about name server capabilities that was dynamically acquired. For example, a name server has been upgraded to support extension mechanisms for DNS (EDNS0). Issue the REFRESH command to reset the current information about the capability of the name server, forcing the z/OS resolver to dynamically determine the new capability.

Clears message EZD2037E from the network operator console. Issue the REFRESH command to restart the resolver unresponsive name server monitoring functions after the resolver had stopped them as a result of a system error.

Restriction: The REFRESH command resets information about all name servers.

The z/OS resolver uses EDNS0 to accept DNS UDP messages that have a length greater than 512 bytes when the name server also supports EDNS0. Using the less costly UDP protocol, EDNS0 results in improved DNS and resolver performance. See the information about Extension Mechanisms for DNS standards and the resolver in z/OS Communications Server: IP Configuration Guide for more details.

In some cases, the resolver statistics regarding name server responsiveness for all name servers are affected by a REFRESH command. This situation occurs when the REFRESH command is used to stop the name server monitoring functions or when the REFRESH command is used to switch between the autonomic quiescing of unresponsive name server function and the network operator notification function. In these situations, the resolver statistics are set to the value of 0 and the current unresponsive name server notification messages EZZ9308E or EZZ9311E are cleared from the operator console. If the REFRESH command does not result in any changes to the unresponsive name server monitoring function, the resolver statistics are not affected and the current unresponsive name server notification messages remain on the operator console. For information about when the statistics and messages are affected, see UNRESPONSIVETHRESHOLD statement in z/OS Communications Server: IP Configuration Reference.

If the REFRESH command is used to change the NSINTERADDR statement values coded in the TCPIP.DATA file specified on the GLOBALTCPIPDATA resolver setup statement, the resolver statistics regarding name server responsiveness for a single name server might be affected. If the REFRESH command is used to remove an unresponsive name server from the NSINTERADDR statements, the resolver will zero the resolver statistics for this name server, will stop sending resolver DNS polling queries to the name server, and will clear the EZZ9311E unresponsive name server notification message from the operator console. For information on the NSINTERADDR statement, see NSINTERADDR statement in z/OS Communications Server: IP Configuration Reference.

SETUP=

The contents of the specified resolver setup file are processed. Processing TCPIP.DATA statements and local host tables are updated at the next resolver request.

Result: If the resolver setup file contains unrecognized resolver setup statements, or setup statements with syntax errors, the MODIFY command fails. The resolver configuration is unchanged.

xxx

Identifies a specific MVS™ sequential data set. The data set must have an LRECL in the range 56–256. The record format can be either RECFM=F or RECFM=FB.

xxx(yyy)

Identifies a specific MVS PDS member. The PDS must have an LRECL in the range 56–256. The record format can be either RECFM=F or RECFM=FB.

'/xxx'

The full path name of the file must be specified and must begin with a slash (/) character. The single quotation marks (') are required around the complete z/OS UNIX file system name so that z/OS command processing passes the file name without changing it to uppercase.

Rule: If the single quotation mark notation is used to specify an MVS data set name, the data set name must be entered in uppercase.

Usage

See the resolver setup statements in the resolver setup file topic in z/OS Communications Server: IP Configuration Guide for an explanation of the fields on the report.