The Network Print Facility uses a routing file or table to determine where to route output that will be processed on remote printers. The routing file is a VSAM key-sequenced data set that contains information to route each data set to its LPD printer queue. You need one routing file entry (VSAM record) for each printer being used at the installation. Each routing file record is identified with a unique key field consisting of a major name and a minor name. For JES printers, the JCL DEST, CLASS, and FORMS parameters are used for the routing file key fields. For VTAM® printers, LU name of the logical printer is used.

The routing file records contain a pointer to options file records. Multiple routing file records can point to the same record in the options file. Because the same destination printer can be used to print output with different characteristics, it can have many entries in the routing file. Each variation will require a separate routing file record pointing to the appropriate LPR options.

You can use the ISPF interface to modify the routing file when changes are required in your network, such as when printers are added or removed. This can be very useful if the network or a workstation stops functioning and the network administrator wants to reroute printer output.

Optionally, instead of altering the routing file, you can change the routing mechanism with a user exit. Use of any exit should not be done casually because it enables you to completely alter the data. See Writing the general routing exit and Writing the specific routing exit for more information on user-defined routing.