Based on the network provided in the exhibit, in these two areas, all routers are performing OSPF
on all interfaces. After examining the OSPF database on R4, do you know which type of LSA will
contain 10.1.5.0/24, and which router will have originated it?
A.
10.1.5.0/24 will be in a summary (type 3) LSA originated by R3.
B.
10.1.5.0/24 will be in a router (type 1) LSA generated by R3.
C.
10.1.5.0/24 will be in a network (type 2) LSA originated by R3.
D.
10.1.5.0/24 will not be in any LSA in the OSPF database at R4, because R4 and R3 are in
different areas.
Explanation:
R3 is an Area Boarder router and ABR advertise Type 3 Summary LSA’s
Type 1 – Router LSA – the router announces its presence and lists the links to other routers or
networks in the same area, together with the metrics to them. Type 1 LSAs are flooded across
their own area only. The linkstate
ID of the type 1 LSA is the originating router ID.
Type 2 – Network LSA – the designated router (DR) on a broadcast segment (e.g. Ethernet) lists
which routers are joined together by the segment. Type 2 LSAs are flooded across their own area
only. The link-state ID of the type 2 LSA is the IP interface address of the DR.
Type 3 – Summary LSA – an Area Border Router (ABR) takes information it has learned on one of
its attached areas and it can summarize it (but not by default) before sending it out on other areas
it is connected to. This summarization helps provide scalability by removing detailed topology
information for other areas, because their routing information is summarized into just an address
prefix and metric. The summarization process can also be configured to remove a lot of detailedaddress prefixes and replace them with a single summary prefix, also helping scalability. The linkstate ID is the destination network number for type 3 LSAs.
http://en.wikipedia.org/wiki/Link-state_advertisement