Which modules must be installed in the MVS link pack area?

The CICS® modules that must be in the MVS™ link pack area are listed.

Table 1. CICS modules required in the LPA
Module Description When required in LPA See notes after this table
DFHCSVC CICS Type 3 SVC Always 1, 2, 4, and 6
DFHDSPEX CICS postexit stub Always 1, 3, and 5
DFHDUMPX SDUMPX IEASDUMP QUERY exit Always 1 and 3
DFHIRP Interregion communication program To use MRO, EXCI, or the console message-handling facility 1, 2, and 6
DFHSSEN Subsystem interface end-of-memory and end-of-task clean up routine To use the console message-handling facility 1, 3, and 6
DFHSSGC Subsystem generic connect module To use the console message-handling facility 3 and 7
DFHSSWT Subsystem interface WTO router To use the console message-handling facility 3 and 7
DFH99SVC Dynamic allocation - SVC services Always 1 and 3
  1. The module can be used only from the MVS link pack area and you must install it there before CICS can be started.
  2. You must always install the latest service level of the modules DFHCSVC and DFHIRP (if required). The version of the modules supplied with the current release is downward-compatible with earlier releases of CICS. It works correctly with CICS regions running earlier releases. Therefore, if you are running different releases of CICS on the same MVS image, use the latest version of the modules.
  3. There is no requirement to use the latest version of this module. The version supplied with the current release is the same as in previous releases.
  4. You must define the DFHCSVC module to MVS as a Type 3 SVC. The default SVC number is 216. If you use a non-default SVC number, you must define it to CICS on the CICSSVC system initialization parameter.
    Moving DFHCSVC into the MVS link pack area:

    Do not use the link editor to install the CICS SVC module into a library in the MVS link pack area. To copy or move the module from the hlq.SDFHAUTH library to the nominated library in the MVS link pack area, use either a suitable copy utility program, such as IEBCOPY, or an SMP/E USERMOD with ++MOVE statements.

  5. The DFHDSPEX module must be in the MVS link pack area for integrity reasons, but the postexit routine, DFHDSAUT, can be either in the MVS link pack area or in the CICS address space. This choice enables you to use different levels of the DFHDSAUT module in different CICS regions running in the same MVS image, because the DFHDSAUT module might not be compatible between CICS versions.
  6. To communicate by MRO, all CICS regions in the same MVS image must use the latest level of the modules DFHCSVC and DFHIRP in the MVS link pack area.

    If a region detects that DFHIRP is at a lower level when it attempts to open interregion communication, it issues message DFHIR3799 and interregion communication fails to open.

  7. To use console message-handling, these modules must be either in the MVS link pack area or in an APF-authorized library in the MVS linklist.

If an LPA module is only ever referred to by name, then refreshing it in the LPA is valid. That is, if each time it is used, a new reference to it is obtained by using an MVS LOAD macro. However, most references to LPA modules do not work this way. The address of an LPA module could be saved into a control block after the initial LOAD of the module. The implication is that this address remains unchanged without a CLPA IPL. If dynamic LPA is used to pick up a change to an LPA module, then the address saved in the control block is no longer valid. Of the 8 CICS modules which must be installed in the LPA, only DFH99SVC is eligible to be refreshed in this way.