Host groups

The host_group statement identifies the set of IP addresses to update in a name server that represents a group of hosts. ADNR updates the name server with the intersection between the IP addresses configured to ADNR in the host_group statement and the IP addresses that exist in the home lists of the hosts in the sysplex. The DNS names that are dynamically added to the name server take the form host_group_name.domain_suffix, where host_group_name is the ADNR administrator-defined name of the group of hosts being registered to the GWM, and domain_suffix is the domain suffix name specified in a zone parameter on a dns statement. To construct the DNS name, the value of the host_group_name keyword of the host_group statement is used, followed by the value of the domain_suffix keyword of the zone referenced in the host_group statement. The intervening dot is supplied by ADNR; do not explicitly code the dot.

ADNR can also update name servers with DNS names representing individual host instances within the sysplex, using the member keyword. ADNR updates name servers with the intersection between the IP addresses configured for the member and the set of IP addresses that exist in the home list of a particular host in the sysplex. The DNS names that are dynamically added to the name server take the form host_name.domain_suffix, where host_name is the ADNR administrator-defined name of the member being registered to the GWM, and domain_suffix is the domain suffix name specified in a zone parameter on a dns statement. To construct the DNS name, the value of the host_name keyword of the host_group statement is used, followed by the value of the domain_suffix keyword of the zone referenced in the host_group statement. The intervening dot is supplied by ADNR; do not explicitly code the dot. If the host_group statement contains a member keyword containing an optional host_name parameter, the name server is updated with these types of DNS names.

A host_group statement can have multiple member keywords within it. One of the coded member keywords does not have to have a host_name parameter. The member without a host_name parameter is sometimes referred to as the unnamed member, while members with a host_name parameter are sometimes referred to as named members. The IP addresses associated with the unnamed member are ones that can potentially be dynamically added to the name server with the DNS name of the form host_group_name.domain_suffix. Configuring an unnamed member is not required. However, a virtual unnamed member is created for you if you do not configure one.

Result: The IP addresses associated with the unnamed member are the union of all IP addresses explicitly configured in the unnamed member (if configured), and all IP addresses configured to all named members in that host group. In contrast, only the IP addresses explicitly configured in a named member are associated with the named member.

Typically, you configure one named member per system in the sysplex. Each named member contains IP addresses that cannot move to other systems in the sysplex.

Guideline: To provide reachability to the sysplex or system in case of interface failure, configure named members of host_group statements with static VIPAs. In addition, you can also code an unnamed member, and associate with it IP addresses that could potentially be moved from one system to another (DVIPAs).

Host names added to a name server using ADNR might be useful for situations when you want connectivity to the sysplex or a host in the sysplex, but the presence of a particular server is not required. For this reason, host group names would be useful for utilities such as ping or traceroute.