Group TCP/IP access

The preferred method of connecting to a data sharing group is to use dynamic virtual IP address (DVIPA) network addressing.

About dynamic virtual IP addressing (DVIPA)

DVIPA gives you the ability to assign a specific virtual IP address to a data sharing group and to each member of the group. This address is independent of any specific TCP/IP stack within the Parallel Sysplex®. Even if a member is moved to another z/OS® system, as in the case of a failure or maintenance, the member remains accessible and retains the same virtual IP address.

The TCP/IP sysplex distributor can play a role in DVIPA network addressing. If the Db2 group DVIPA is configured to distribute connections across all members that are listening to the Db2 DRDA PORT, the sysplex distributor can factor real-time information, such as member status and Quality of Service (QoS) data. This type of group DVIPA is called a distributing DVIPA or DDVIPA. This data, along with information that is obtained from the Workload Manager (WLM), ensures that the best member is chosen to serve each client connection request.

If the group DVIPA is configured to distribute connections by using the sysplex distributor, when the application specifies the Db2 location that maps to a group DVIPA, the sysplex distributor dispatches the requester's initial connection request to the active member with the most capacity. The requester ensures that workload balancing is invoked as follows:
  • Requests are always routed to an active member, if at least one member is active.
  • Requests are dynamically directed to those members that are using WLM system weights if you are using the default distribution method.

Sysplex workload balancing functionality on Db2 for z/OS servers provides high availability for client applications that connect directly to a data sharing group. Sysplex workload balancing functionality provides workload balancing and automatic client reroute capability. This support is available for applications that use Java™ clients (JDBC, SQLJ, or pureQuery®), or non-Java clients (ODBC, CLI, .NET, OLE DB, PHP, Ruby, or embedded SQL). For more information, see Java client direct connect support for high availability for connections to Db2 for z/OS servers and Non-Java client support for high availability for connections to Db2 for z/OS servers.

DVIPA and failure recovery

Using DVIPA is the most flexible way to be prepared for Db2 or system failure. If at least one member of a data sharing group is active and can perform work, connection attempts of requesters do not fail.

If a member suffers a failure or the underlying z/OS system suffers an outage, automation software such as z/OS Automatic Recovery Manager (ARM) can restart the member on a different z/OS system. When this type of restart happens, the member-specific DVIPA is also moved to the new system and automatic recovery of any indoubt threads is performed, thereby enabling requesters to access the member on the new z/OS system.

Requirements and considerations

  • If you plan to use DVIPA network addressing, check with your network administrator to determine whether DVIPA can be configured for the Parallel Sysplex. DVIPA network addressing is required if you are using clients that support Sysplex workload balancing. You also must use DVIPA network addressing to support remote XA connections.
  • Ensure that the following conditions exist before making a data sharing group available for group access that uses DVIPA network addressing:
    • All members of the group are configured with DVIPAs before starting the DDF on any member of the group.
    • All members of the group are configured with DVIPAs before remote connections are made to any member of the group.
  • Before moving to DVIPA network addressing from another access method, have all members check for the existence of indoubt threads. If any indoubt threads exist, resolve them before moving. To check for indoubt threads, use the DISPLAY THREAD command.
  • DVIPA network addressing requires you to define multiple DVIPAs, one for the data sharing group and one for each member of the group.
    • The group DVIPA is common to all members of the group, and it is used to make the initial connection to a member of the group. The group DVIPA should be owned and managed by the sysplex distributor, which provides workload balancing among members during new connection request processing.
    • Every member of the group needs a unique DVIPA, which is used to directly connect to a particular member after the initial connection. Configure DVIPAs for each member of the data sharing group that can be started.
  • Db2 supports two methods for specifying DVIPAs: the BSDS (INADDR_ANY) method and the BINDSPECIFIC method. Each method has different characteristics that might make one method more appropriate for your environment than the other method. See Supported methods for specifying DVIPAs to determine which method is best for your environment.