Resolver address space

The statements found in a resolver configuration file can be globally overridden at the z/OS level by the resolver address space.

When an application needs to access services identified within the resolver configuration file, it is accomplished using the resolver started task (address space). The resolver address space is normally started when z/OS is started. The significance of this resolver address space is that the address space itself can be configured with resolver configuration file statements.

These statements can be used to provide resolver configuration file settings for both z/OS UNIX applications and MVS applications. A sample of the JCL for starting the resolver configuration file is shown in Figure 1. Again, this JCL is only a portion of the JCL required.

Figure 1. Sample JCL for starting resolver address space

 //RESOLVER PROC PARMS='CTRACE(CTIRES00)'
 //EZBREINI EXEC PGM=EZBREINI,REGION=0M,TIME=1440,PARM=&PARMS
 //SETUP    DD   PATH='/etc/setup.resolver',PATHOPTS=(ORDONLY)

The statement of interest in Figure 1 is the SETUP DD statement. This DD points to a file containing statements controlling the behavior of resolver configuration file searches. There are several statements available within a resolver configuration SETUP file.

Two more important statements are:

GLOBALTCPIPDATA: This statement is used to identify a specific resolver configuration file that contains the resolver configuration statements (NAMESERVER, HOSTNAME, and so on) that are to be applied globally to all IP applications.
DEFAULTTCPIPDATA: This statement is used to define a default resolver configuration file that is used as a last resort.

Note: Hopefully, that SETUP DD statement in Figure 1 has not confused you. A DD statement can point to a z/OS UNIX file in the HFS as well as to a z/OS data set.

In this example, there is no particular reason why an HFS file was chosen; it could just as easily have been a z/OS data set or a data set member.