Sysplex subplexing

VTAM® participates in the sysplex environment through two sysplex groups:

The XCF group is used for dynamic definition of VTAM-to-VTAM connections.
The CFS group is used for VTAM coupling facility services.

You partition VTAMs in the sysplex into subsets (subplexes) by modifying the names of the two sysplex groups that the sysplex joins. Use subplexing to separate and isolate the XCF connectivity of sets of VTAM nodes in the sysplex. VTAMs using the same XCF group name and the same CFS group name are in one subplex, and VTAMs with a different XCF group name and CFS group name are in a different subplex.

Modify the group names that VTAM uses with the XCFGRPID start option. VTAM joins the XCF group with a name in the format ISTXCFvv and it joins the CFS group with a name in the format ISTCFSvv, where vv is the numeric 2-digit value you supply on the XCFGRPID start option. The value specified for vv must be in the range 02-31. If you specify a single digit in the range 2-9, the value is padded on the left with 0. If you do not supply an XCFGRPID value, the XCF group name is ISTXCF and the CFS group name is ISTCFS01.

TCP/IP stacks can also be partitioned into subsets (subplexes) within the sysplex by specifying the XCFGRPID parameter on the GLOBALCONFIG statement in the TCP/IP profile. Because the TCP/IP stack relies on VTAM support for its XCF connectivity, TCP/IP subplexes cannot span VTAM subplexes. That is, two TCP/IP stacks in the same subplex cannot be in different VTAM subplexes. To enforce this, the sysplex group that TCP/IP joins in the sysplex has a name in the format EZBTvvtt, where vv is the VTAM group ID suffix you specified on the XCFGRPID start option, and tt is the TCP/IP group ID suffix value you specified on the XCFGRPID parameter on the GLOBALCONFIG statement. For example, if VTAM is started with a value of XCFGRPID=11, and a TCP/IP stack is started with a GLOBALCONFIG statement specifying XCFGRPID=21, the corresponding TCP/IP sysplex group name is EZBT1121.

If VTAM is stopped and restarted with a different value for the XCFGRPID parameter, the TCP/IP stacks that use that VTAM must also be stopped and restarted to pick up the new VTAM subplex suffix.

Because subplexing separates XCF connectivity, the VTAM and TCP/IP coupling facility structures that are accessed must be separated by subplexing.

For the VTAM structures (for generic resources and MNPS), VTAM appends the VTAM XCFGRPID suffix to the end of the name specified on the STRGR and STRMNPS start options (or on ISTGENERIC and ISTMNPS, if the names are the default values). Thus, using the previous example, if you specify STRGR=ISTMYGR and STRMNPS=ISTMYMNPS as start options, and you also specify XCFGRPID=11, VTAM would attempt to connect to the structures ISTMYGR11 and ISTMYMNPS11. The fully suffixed MNPS and generic resources structure names can be displayed by issuing the D NET,ID=VTAM command.
For the TCP/IP structures (for SWSA and sysplexports), VTAM appends the VTAM XCFGRPID suffix, followed by the TCP/IP XCFGRPID suffix to the end of the base structure names to create the separation. The base structure name for SWSA is EZBDVIPA and the base structure name for sysplexports is EZBEPORT. Again, using the previous example, TCP establishes connectivity to structures EZBDVIPA1121 and EZBEPORT1121.

Note: Any system in the sysplex that has access to the coupling facilities can be picked as a monitor for sysplex processing, and this has operational implications affecting how certain messages are processed. It is possible that the XCF monitor processing could be issuing messages on a system in 'subplex a' for a system that resides in 'subplex b'.

References to the base group names, ISTXCF, ISTCFS01, EZBTCPCS, and the base structure names, ISTGENERIC, ISTMNPS, EZBDVIPA, and EZBEPORT reference the fully suffixed names, if subplexing is used.