• Storing hundreds of external routes on an edge router with a single path out consumes CPU and RAM for zero operational gain.
    Converting Area 2 into a Stub Area eliminates this unnecessary control plane overhead.

    The Lab Topology

    Look at the layout:

    OSPF lab topology with four routers across Area 1, Area 0 and Area 2, and an external autonomous system connected to R1

    Figure 1 – The lab topology

    • R2 and R3 act as Area Border Routers (ABRs).

    • R4 sits at the edge of Area 2 as a single-homed branch router.

    Creating External Routes

    R1 connects to the external autonomous system and learns 204 networks in the 172.16.0.0/16 range via eBGP.

    R1 labeled as ASBR flooding Type 5 LSAs while R2 and R3 are labeled as ABRs between Area 1, Area 0 and Area 2

    Figure 2 – R1 becomes an ASBR

    Redistributing BGP into OSPF turns R1 into an ASBR.
    It generates a Type 5 LSA for every external network:

    R1# configure terminal
R1(config)# router ospf 1
R1(config-router)# redistribute bgp 65000 subnets
R1(config-router)# end

    By default, every router across all areas receives these 204 Type 5 LSAs and populates its routing table with individual external entries.

    Answer the question below

    Which LSA type does R1 generate for the redistributed networks?