Challenge: 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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Re: Challenge: How are routes propagated in OSPF Transit Area?
 

The packets go through the path : R5.5.5.5 > R4.4.4.4 > R1.1.1.1

Re: Challenge: How are routes propagated in OSPF Transit Area?
 

The packets go through the Path: R5.5.5.5 > R4.4.4.4 > R1.1.1.1 because the lowest cost of the route through this path, if you check the routing table of R4.4.4.4,it has a best route toward the subnet 1.1.12.0 through R1.

Re: Challenge: How are routes propagated in OSPF Transit Area?
 

Hi redouane,

You are correct, the correct path is R5.5.5.5 > R4.4.4.4 > R1.1.1.1.

By default for Cisco routers, the OSPF Area Transit Capability feature is enabled. Allowing OSPF Area Border Router (ABR) to discover shorter paths through the transit area for traffic forwarding that would normally need to travel through the virtual-link path.

For more details, feel free to check out the answer page.