DNS network addressing

A domain name server (DNS) provides standard name resolution services for IP applications in a Parallel Sysplex® cluster, converting domain names into IP addresses.

If, in its connection request, an application specifies a Db2 location name that maps to a group domain name, the requester queries the DNS with a call to gethostbyname. Either the DNS resolves the name to a member's IP address, or it resolves the name to a list of member IP addresses. The DNS returns the IP address or list of IP addresses to the requester, which then uses it to make an initial connection to a member of the data sharing group.

If your DNS supports it, and the Sysplex Distributor is not used to manage the group's DVIPA, configure the DNS to return a list of member IP addresses (member DVIPAs) instead of returning a single IP address. The list includes member IP addresses and ports, and a weight for each active member that indicates the member's current capacity. The requester uses the returned information to connect to the member with the most capacity. If you use the Sysplex Distributor to manage the DVIPA of the group, configure the DNS to return the group DVIPA.

Recommendation: If your DNS supports it, configure the DNS to return a list of member IP addresses instead of returning a single IP address. Because a DNS does not know whether a member is active when it returns the member's IP address to the requester, the DNS might return the IP address of an inactive member. Using this IP address on a subsequent connection request causes the request to fail. In contrast, if you configure the DNS to return a list of member IP addresses, the connection request can be retried using another IP address on the list. When the DNS retries the connection request, it will run through the list once, searching for the active member.