Configuring subsets for member-specific access

Db2 for z/OS® allows you to define subsets of data sharing group members in TCP/IP networks for member-specific access.

About this task

By designating subsets of members, you can:

Limit the members to which DRDA requesters can connect.
System and database administrators might find this useful for any number of purposes.
Ensure that initial connections are established only with members that belong to the specified subset.
Without subsets, requesters can make initial and subsequent connections to any member of the data sharing group.
Provide requesters with information about only those members in the subset.
With subsets, a member that receives an initial connection request can return to the requester a list of members that are currently active, able to perform work, and represented by the location alias.

Procedure

To configure a subset for member-specific access:

Complete one of the following actions:

Use the MODIFY DDF command to modify member specific location aliases without stopping Db2. For example, to modify the port number used by a member for an alias ALIAS1, you would issue the following sequence of commands.
1. Issue a MODIFY DDF command to stop the alias:
```
MODIFY DDF ALIAS (ALIAS1) STOP
```
2. Issue a MODIFY DDF command to modify the member-specific alias port:
```
MODIFY DDF ALIAS (ALIAS1) PORT (447)
```
  You can also add new aliases and define, modify, and remove SECPORT, IPV4 and IPV6 values for an existing alias.
3. Issue a MODIFY DDF command to start the alias:
```
MODIFY DDF ALIAS (ALIAS1) START
```
  - If any ports are specified for the alias, DDF registers any subset location aliases with z/OS Workload Manager (WLM). The list of members in the subset is managed automatically by z/OS.
  - DDF adds the TCP/IP port numbers of the subset location aliases to a TCP/IP SELECT socket call for the SQL request listener. Doing so enables the sysplex distributor to send requests that are intended for subset members to only those members that belong to the subset. It also enables members of the subset to respond to those requests.
Stop Db2 and invoke the DSNJU003 utility and specify the alias-port parameter of the ALIAS option of the DSNJU003 (change log inventory) utility. When you start DDF, it performs the following tasks:
- If any ports are specified for an alias, DDF registers any subset location aliases with z/OS Workload Manager (WLM). The list of members in the subset is managed automatically by z/OS.
- DDF listens for SQL requests on the alias ports specified for each subset that it is part of. This enables members of a subset identified by an alias name to respond to SQL requests to that particular alias, either coming in directly from a remote client or through the sysplex Distributor.