The resolver

The resolver acts on behalf of programs as a client to perform the following functions:

• Access name servers to provide name-to-address or address-to-name resolution
• Allocate and read the TCPIP.DATA file
• Establish TCP/IP stack affinity for certain socket APIs
• Provide protocol and services information

To resolve the query for the requesting program, the resolver uses information that it obtains from the following sources:

• Available name servers
• The DNS response information that has been cached locally (when system-wide caching is enabled)
• Local definitions, such as /etc/hosts, /etc/ipnodes, HOSTS.SITEINFO, HOSTS.ADDRINFO, and ETC.IPNODES

The TCPIP.DATA statements control how (and if) the resolver uses name servers. For detailed information about TCPIP.DATA configuration statements, see z/OS Communications Server: IP Configuration Reference.