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RouterA and RouterB are both in OSPF area 2, and RouterA is connected directly to the backbone. Their
router IDs are shown below:
RouterA – 165.165.20.15
RouterB – 165.165.10.12
Which commands should be executed on RouterA and RouterB to create a virtual link between the two
routers?

A. RouterA(config-router)# area 2 virtual-link 165.165.10.12
RouterB(config-router)# area 2 virtual-link 165.165.20.15

B. RouterA(config-router)# area 2 virtual-link 165.165.10.12
RouterB(config-router)# area 0 virtual-link 165.165.20.15

C. RouterA(config-router)# area 0 virtual-link 165.165.20.15
RouterB(config-router)# area 2 virtual-link 165.165.10.12

D. RouterA(config-router)# area 0 virtual-link 165.165.10.12
RouterB(config-router)# area 0 virtual-link 165.165.20.15

Explanation:
The area virtual-link command should specify the area to be traversed and the ID of the router to which the
router being configured will connect. Therefore, the correct answer is:
RouterA(config-router)# area 2 virtual-link 165.165.10.12
RouterB(config-router)# area 2 virtual-link 165.165.20.15

A virtual link is used to make a virtual connection of an area border router (ABR) to the backbone. It is used
in situations where an area does not physically border the backbone area. The virtual link provides logical
connectivity of the area to the backbone. If the virtual link appears not to be functional, which would
manifest itself in Router A not having all of Router B’s networks in its routing table, the state of the link can
be verified on Router A by executing the show ip ospf virtual-link command. An example is shown below.
The state of the link as shown in line 1 of the output should be up.
RouterA# show ip ospf virtual-links
Virtual Link to router 172.16.8.2 is up
Transit area 0.0.0.1, via interface Ethernet0, Cost of using 10
Transmit Delay is 1 sec, State POINT_TO_POINT
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 0:00:08
Adjacency State FULL
The configuration below is incorrect because area 0 is referenced in the second line. It should reference
area 2, the area being traversed.
RouterA(config-router)# area 2 virtual-link 165.165.10.12
RouterB(config-router)# area 0 virtual-link 165.165.20.15

The configuration below is incorrect because area 0 is referenced in the first line. It should reference area 2,
the area being traversed.
RouterA(config-router)# area 0 virtual-link 165.165.20.15
RouterB(config-router)# area 2 virtual-link 165.165.10.12

The configuration below is incorrect because area 0 is referenced in both lines. Both should reference area
2, the area being traversed.
RouterA(config-router)# area 0 virtual-link 165.165.10.12
RouterB(config-router)# area 0 virtual-link 165.165.20.15

If the virtual link is incorrectly configured the following error will be generated:
*Dec 10 00:31.146: %OSPF-4-ERRRCV: Received invalid packet mismatch area ID,
from backbone area must be virtual link but not found from 165.165.10.5, Serial
0
Objective:

Layer 3 Technologies
Sub-Objective:
Configure and verify network types, area types, and router types
References:
Cisco > Home > Support > Technology Support > IP Routing > Design > Design Technotes > What Are
OSPF Areas and Virtual Links?

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