Hello James
When implementing the area 1 virtual-link command, we don’t indicate the router on the other end of the virtual link with an IP address of an interface, but with the router ID. Notice that before the virtual link commands are implemented, the following show commands were used to determine the router IDs:
It is these two router IDs that are being used in the subsequent virtual-link commands. Note that initially, the virtual link is down because the router with ID 1.1.1.1 does not know how to reach the router with ID 192.168.23.3 (the other end of the virtual link). All of the link-state advertisements (LSAs) in Area 1 need to be flooded, and the shortest path first (SPF) algorithm must be run within Area 1 by both routers so that the two routers will know how to reach each other through area 1. The actual IP addresses used to communicate and to create the virtual link will be 192.168.12.1 and 192.168.23.3.
I hope this has been helpful!
Laz