This page describes setup of DNS on a system with a single TCPIP stack.

DNS settings on z/OS are managed by RESOLVER address space.

Resolver started task has a config DD - SETUP. It points to a dataset with global parameters. SETUP dataset points to TCPDATA configuration - GLOBALTCPIPDATA. If some TCPDATA is not defined there, RESOLVER searches for them in this order - https://www.ibm.com/docs/en/zos-basic-skills?topic=information-search-order-resolver-configuration

In TCPDATA config member we can define GLOBALIPNODES - dataset or uss member which will contain the hard-coded IP addresses and host names to be used on the system.

After applying changes RESOLVER address space must be restarted. But once you stop it - you’ll loose connection to a system if you use a hostname (not ip address). One option is to connect directly by the ip address. Another option is to use a started task with coded /p RESOLVER and /s RESOLVER statements.