OSPF Advanced Virtual Link configuration: Multiple Virtual-Link

At this level I suppose you know how to configure the Virtual Link, and what is it's purpose. Let's get some deeper into clearing out some doubts.

1. What happens with the OSPF Neighbors, and how do I check the Virtual Link?
Configure between two routers out of which none is in the Area 0 (Backbone Area). Once it's configured - a new OSPF neighbor will be added as a Virtual-Link neighbor:

Cisqueros_R3#show ip ospf neighbor 

Neighbor ID     Pri   State           Dead Time   Address         Interface
4.4.4.4           0   FULL/  -        00:00:05    10.1.34.4       OSPF_VL0 <--- VIRTUAL LINK NEIGHBOR
2.2.2.2           0   FULL/  -        00:00:30    10.1.23.2       Serial1/0.32
4.4.4.4           0   FULL/  -        00:00:34    10.1.34.4       Serial1/0.34


2. What do I do if I have more areas connected to each other, but none connected to Area 0. Can I form multiple Virtual Links?

The answer is YES, you can! So for example if we have the following scenario:

Cisqueros_R1 - Area 0 - Cisqueros_R2 - Area 1 - Cisqueros_R3 - Area 2 - Cisqueros_R4 - Area 3 - Cisqueros_R5

We would need to create 2 virtual links
 - AREA 1 VIRTUAL LINK between Cisqueros_R2 and Cisqueros_R3 so that Area 2 would have the communication with the Area 0
 - AREA 2 VIRTUAL LINK between Cisqueros_R3 and Cisqueros_R4 so that Area 3 could communicate with Area 1, and therefore with Area 0

 Cisqueros_R2:
 (config-router)#area 1 virtual-link 3.3.3.3

 Cisqueros_R3:
 (config-router)#area 1 virtual-link 2.2.2.2
 (config-router)#area 2 virtual-link 4.4.4.4

 Cisqueros_R4:
 (config-router)#area 2 virtual-link 3.3.3.3

Let's check the OSPF Neighbors again on Cisqueros_R3 router:

Cisqueros_R3#show ip ospf neighbor 

Neighbor ID     Pri   State           Dead Time   Address         Interface
2.2.2.2           0   FULL/  -           -        10.1.23.2       OSPF_VL1
4.4.4.4           0   FULL/  -           -        10.1.34.4       OSPF_VL0
2.2.2.2           0   FULL/  -        00:00:34    10.1.23.2       Serial1/0.32
4.4.4.4           0   FULL/  -        00:00:33    10.1.34.4       Serial1/0.34
Cisqueros_R3#

Check the Virtual Link Details:

#show ip ospf virtual-links  

Have in mind that routers Cisqueros_R3 and Cisqueros_R4 are now VIRTUALLY connected to Area 0, so if you enable the authentication on the Cisqueros_R1 interface towards Cisqueros_R2, you also must enable authentication for Area 0 on Cisqueros_R3 and Cisqueros_R4!!!