• In a multi-area OSPF network, every non-backbone area must be directly connected to Area 0.
    In our topology below, this rule is broken!

    OSPF multi-area topology with Area 0 backbone, Area 1 and Area 2 across five routers

    Figure 1 - OSPF Multi-Area Topology

    As you can see, Area 2 is connected only to Area 1.
    This creates a fundamental routing problem: inter-area traffic must always travel through the backbone (Area 0).

    OSPF Area 2 not connected to Area 0 backbone while Area 1 is connected through the ABR

    Figure 2 - Area 2 is not connected to Area 0

    Because R4 has no active interface in Area 0, the networks of Area 2 can never be advertised into the backbone. The rest of the network will never learn them.

    In this scenario, you can use an OSPF feature called a Virtual Link (VL) to resolve the issue without adding physical links. Let's take a look together.

    Answer the question below

    Which area is not connected to the backbone?