TCP/IP access methods for Db2 data sharing

TCP/IP is a set of communication protocols that support peer-to-peer connectivity functions for both local and wide area networks. TCP/IP uses the client/server model of communication to enable communication between computers and computer networks of the same or different types.

TCP/IP uses the client-server model of communication to enable communication between computers and computer networks of the same or different types. On the sending end, Transmission Control Protocol (TCP) manages the assembly of a message or file into smaller packets that are transmitted over a network. On the receiving end, TCP manages the re-assembly of those packets into the original message or file. Internet Protocol (IP) handles the routing of each packet, ensuring that packets reach the correct destination.

Tip: TCP/IP is the recommended communication protocol for communication with Db2. Although SNA communication remains supported in Db2 13, SNA communication (including the VTAM interface) is deprecated, and support might be removed in the future. You can disable SNA communication by setting the value of the DB2 TCP/IP IPNAME setting. See DB2 TCP/IP IPNAME field.

It is strongly recommended that when setting up the IP addresses to be used by a specific member of a data sharing group, that the IP address be a dynamic Virtual IP Address (DVIPA). By using such a capability, the specific Db2 member of the data sharing group is "assigned" its own IP address no matter where in the Sysplex the Db2 subsystem is started. This process will then permit successful automatic handling of indoubt units-of-work during subsystem restart or recovery especially when that member of the data sharing group is being accessed by requesters operating under the control of XA transaction managers and two-phase commit transaction coordinators.

When considering the use of a data sharing group IP address, you can only use a DVIPA which is being managed by the Sysplex Distributor. If you attempt to use a DVIPA that is not managed by the Sysplex Distributor or any other address as the group IP address, only one member of the data sharing group can be reached via that address. This process defeats the purpose of a common IP address that can be used to access any member of the data sharing group.

A TCP/IP requester can use one of several access methods to connect to a data sharing group:
Group access
A requester uses the group's dynamic virtual IP address (DVIPA) to make an initial connection to the Db2 location. Accessing the Db2 group using the group IP address is always successful if at least one member is started. If the Sysplex distributor is configured for the group IP address, the initial connection is based on the routing algorithm used by the Sysplex Distributor.

Alternatively, a requester can use a domain name, which is set up to return a list of member IP addresses. The requester will attempt to open a connection using every IP address in the list until the connection is successful.

If the requester is enabled for sysplex workload balancing, the initial connection returns a list of members that are currently active and the capacity of each member to perform work. The requester uses this information to balance subsequent connections.

If the requester is enabled for connection concentrator support, connections return an updated list members that are currently active and the capacity of each member to perform work. The requester uses this information to route subsequent transactions to the member with the highest capacity. Transactions are processed across the group to provide the best utilization of work across the group.

Member-specific access
A requester uses location alias names, which specifies one or more members of the group, to make an initial connection to one of the members that is represented by the alias names. The member that receives the request returns a list of members that are currently active and able to perform work. The requester uses this information to send subsequent connection and query requests to available members that are represented by the location alias names. A Db2 for z/OS® requester can also use the SYSIBM.IPLIST table to isolate requests to a subset of members using IPLIST or location alias names support to access remote data sharing groups.
Single-member access
A requester uses a member's DVIPA, actual IP address, or domain name to connect and send queries to a single member of the group. All connection and query requests from that requester are directed to the same member.