RESOLVEVIA statement
Use the RESOLVEVIA statement to specify the protocol used by the resolver to communicate with the name server.
Guideline: If you use the autonomic quiescing of unresponsive name servers function, you should use UDP as your protocol to communicate with the name server.
Syntax
.-RESOLVEVIA UDP------. >>-+--------------+--+---------------------+------------------->< '-system_name:-' '-RESOLVEVIA--+-UDP-+-' '-TCP-'
Parameters
- system_name:
- The name of the system to which this statement applies. See system_name considerations for a complete
description of this parameter.
Requirement: The colon is required.
- UDP
- Specifies that the protocol is UDP. The default protocol is UDP.
- TCP
- Specifies that the protocol is TCP.
If anything other than UDP or TCP is specified, the default of UDP is used.
Steps for modifying
You can refresh this statement using the MODIFY command. For more information about parameters used with the MODIFY command, see z/OS Communications Server: IP System Administrator's Commands.
Examples
RESOLVEVIA TCP
Usage notes
When RESOLVEVIA UDP is specified, the resolver primarily uses the UDP protocol but can switch to TCP protocols under certain conditions. The resolver is most likely to switch to TCP protocols when a DNS reply from the name server is truncated. Even though the resolver supports Extension Mechanisms for DNS0 (EDNS0) standards and accepts up to 3072 bytes of reply data, not all DNS name servers support EDNS0. Firewall settings along the path to the name server can also limit the number of bytes in a resolver UDP reply. To maximize the use of UDP protocols by the resolver, configure firewalls such that the TCP and UDP ports to and from the name servers are allowed to pass the larger EDNS0 packets.
For more information about EDNS0 processing, see z/OS Communications Server: IP Configuration Guide.
