OSPF Transit Capability

Case 1:

Virtual link over area 3 between R4 and R1
4.4.4.4/32 on R4 in area 5

-R4 generates LSA3 into area 0 for the area 5 prefix (its lo0), sets the V flag for its router LSAs (in area 3, marking it as "transit")

Capability Transit OFF
-R1 installs the LSA3 from area 0

-R3 installs the LSA3 from area 0 (ignores LSA 3 from non-backbone area, because R3 is an ABR),

-R5 installs the LSA3 from area 3(R4 is an ABR, generating a summary into area 3)





Capability Transit ON
-R1 installs the LSA3 from area 0

-R3 installs the LSA3 from area 3 (because it knows that area 3 is a transit area(loop free), and the path has lower cost(cost on fa0/1 = 22222)

-R5 installs the LSA3 from area 3(R4 is an ABR, generating a summary into area 3)

Case 2:

Virtual link over area 3 between R5 and R3
Virtual link over area 3 between R4 and R1
4.4.4.4/32 on R4 in area 5


Capability Transit OFF
-R5 installs the LSA3 from area 0(R4 is an ABR, generating a summary into area 3, which ends up being ignored by R5, becase R5 is now an ABR)

Capability Transit ON
-R5 installs the LSA3 from area 3(R4 is an ABR, generating a summary into area 3, which gets accepted and installed by R5, because R5 has already seen the Router LSAs with V-bit, being flooded in area 3 by R4(because of its virtual link to the backbone))