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How are routes propagated in OSPF Transit Area?
According to the following diagram, virtual link was configured on R4.4.4.4 and R5.5.5.5 to set up a connection between area 3 and area 0. Area 1 is a transit area.
What would be the path from 50.5.5.5 (Area 3) of R5.5.5.5 to 1.1.12.1 (Area 0) of R1.1.1.1?
| A) | Red Path: R5.5.5.5 > R4.4.4.4 > R1.1.1.1 |
| B) | Blue Path: R5.5.5.5 > R4.4.4.4 > R3.3.3.3 > R2.2.2.2 > R1.1.1.1 |
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Answer:
A) Red Path.
Explanation: The OSPF Area Transit Capability feature is enabled by default in Cisco router. This feature provides an OSPF Area Border Router (ABR) the ability to discover shorter paths through the transit area for forwarding traffic that would normally need to travel through the virtual-link path. This functionality allows Cisco IOS software to be compliant with RFC 2328.
We can verify the path through the trace route result:
To disable transit capability, execute the no capability transit command in the OSPF configuration mode on R4.4.4.4. Then, it will take the Blue path.
