Example 4: Replacing a virtual route in the list

The virtual route selection exit routine receives:

Addresses of descriptor blocks	Descriptor block contents
VR1,TP2 descriptor block	VR1,TP2 . . .
VR2,TP1 descriptor block	VR2,TP1 . . .
VR3,TP0 descriptor block	VR3,TP0 . . .
(*)VR4,TP0 descriptor block	VR4,TP0 . . .

To replace the first entry in the virtual route list, overwrite the contents of the appropriate descriptor block:

Addresses of descriptor blocks	Descriptor block contents
VR1,TP2 descriptor block (This is still the original address; only the contents of the block change, not the address of the block.)	VR6,TP1 . . .
VR2,TP1 descriptor block	VR2,TP1 . . .
VR3,TP0 descriptor block	VR3,TP0 . . .
(*)VR4,TP0 descriptor block	VR4,TP0 . . .

After the replacement, the first address in the list points to the same descriptor block. However, the contents of the descriptor block have been overwritten. The new contents describe VR6,TP1. VTAM® attempts to use VR6,TP1 before using the other virtual routes in the list.
If the virtual route is not valid (defined as being outside the range 0–7 or as having a transmission priority outside the range 0–2) or is not defined between the origin and destination subareas, VTAM continues through the set of virtual routes, attempting to activate the next one in the set (VR2,TP1).