OSPF Dis-contiguous network

Question 1

Discontiguous Network

Answer 1

Most people would assume that R1 would learn about the route learned by Area 45 because R4 is an ABR. However, they would be wrong. ABRs follow three fundamental rules for creating Type 3 LSAs:

• Type 1 LSAs received from an area create Type 3 LSAs into backbone area and nonbackbone areas.
• Type 3 LSAs received from Area 0 are created for the nonbackbone area.
• Type 3 LSAs received from a nonbackbone area are only inserted into the LSDB for the source area. ABRs do not create a Type 3 LSA for the other areas (including a segmented Area 0).

Question 2

Virtual Links

Answer 2

Virtual links are built between routers in the same area. The area in which the virtual link endpoints are established is known as the transit area. Each router identifies the remote router by its RID. The virtual link can be one hop or multiple hops away from the remote device.

You configure the virtual link by using the command area area-id virtual-link endpoint-RID. The configuration is performed on both endpoints of the virtual link. At least one endpoint virtual link router has to be a member of Area 0, and virtual links cannot be formed on any OSPF stubby areas.