The resolver acts on behalf of programs as a client that accesses name servers for name-to-address or address-to-name resolution. The resolver can also be used to provide protocol and services information. 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. How and if the resolver uses name servers is controlled by TCPIP.DATA statements (resolver directives). The resolver address space must be started before any application or TCP/IP stack resolver calls can occur.

This topic explains the format of the resolver data sets and files when they are stored in the z/OS UNIX file system.