The default resolver settings

You do not have to perform any customization steps to use the resolver. The default resolver starts automatically when z/OS® UNIX is initialized; you cannot use automation tools to start the resolver unless you customize it. z/OS UNIX starts a resolver address space, which uses the assigned name RESOLVER, using the system default procedure IEESYSAS. The resolver uses the applicable native MVS™ or z/OS UNIX search order to find TCPIP.DATA statements, without a GLOBALTCPIPDATA or a DEFAULTTCPIPDATA specification.

The following resolver functions are active by default:

• System-wide caching, using the default maximum cache size and the default maximum time-to-live (TTL) value (see Resolver caching)
• Network operator notification of unresponsive Domain Name System (DNS) servers, using the default threshold setting (see Monitoring the responsiveness of Domain Name System name servers)

The Extension Mechanisms for DNS (EDNS0) standards function is always active. For more information, see Extension Mechanisms for DNS standards and the resolver.