CNM routing table

VTAM® uses a communication network management (CNM) routing table to determine which CNM application program is to receive an unsolicited network-services request unit that requires further processing. An application program can embed its own procedure-related identifier (PRID) in each request sent to VTAM. When a reply to the request is returned, VTAM uses the PRID to route the reply to the application program. Unsolicited RUs contain network information but do not contain a PRID. VTAM uses the CNM routing table to determine which application program is to receive the unsolicited RU.

IBM® supplies default routing information for the following CNM application programs:
  • The NetView® program
  • Alias name translation facility (supplied by IBM as part of the NetView program)
  • Downstream load utility

The IBM-supplied CNM routing table is named ISTMGC01. See IBM-supplied CNM routing table for a listing of the IBM-supplied CNM routing table.

For any application other than the default CNMTABLE to route unsolicited RUs to the application program, modify the default and give it a new name. You can name your supplemental table any 1- through 8-character name, but do not use ISTMGC00 as a table name if you are using multiple CNM routing tables because VTAM will always look for ISTMGC001 first and use that when VTAM is starting with a particular set of libraries. You might choose instead to select a 1- through 8-character name and specify the CNMTAB= start option. This allows you to have different CNM tables stored in the same set of VTAM libraries, which results in the following benefits:
  • You can start VTAM with different CNM tables.
  • You can run VTAM with different characteristics at different times.
  • You can run two VTAMs that are different at the same time.
  • You will have an old copy and a backup copy.

If you are starting multiple VTAMs that use the same VTAM library, you can have multiple supplemental CNM routing tables. Use the CNMTAB start option to associate a specific CNM routing table with the VTAM being started.

Whenever VTAM receives an unsolicited RU, VTAM uses the value specified on the CNMTAB start option to route the request.

  • If you do not specify the CNMTAB start option or specify CNMTAB=ISTMGC00, VTAM will use ISTMGC00, if available. No message is issued if ISTMGC00 is not found. In this case, VTAM uses the IBM-supplied table, ISTMGC01.
  • If you specify a name other than ISTMGC00 on the CNMTAB start option and it is not found by VTAM, message IST116I is issued.

Any user-supplied table used by VTAM overrides the IBM supplied table, ISTMGC01.