Understanding resolvers

The resolver acts on behalf of programs as a client that accesses name servers for name-to-address or address-to-name resolution. To resolve the query for the requesting program, the resolver can access available name servers, use local definitions (for example, /etc/resolv.conf, /etc/hosts, /etc/ipnodes, HOSTS.SITEINFO, HOSTS.ADDRINFO or ETC.IPNODES), or use a combination of both.

When the resolver address space starts, it reads an optional resolver setup data set pointed to by the SETUP DD card in the resolver JCL procedure. If the setup information is not provided, the resolver uses the applicable native MVS™ or z/OS® UNIX search order without any GLOBALTCPIPDATA, DEFAULTTCPIPDATA, GLOBALIPNODES, DEFAULTIPNODES or COMMONSEARCH information.