Refer to the Exhibit.
In the exhibit, Areas 1.1.1.1 and 2.2.2.2 are configured as normal areas. R5 has an export policy that causes the RIP network prefixes to be announced through OSPF. Which three LSA types does R7 receive for the information advertised by R5? (Choose three.)
A.
Router (Type 1)
B.
Network (Type 2)
C.
Summary (Type 3)
D.
ASBRSum (Type 4)
E.
External (Type 5)
Explanation:
The LSA types defined in OSPF are as follows: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 detailed address prefixes and replace them with a single summary prefix, also helping scalability. The link-state ID is the destination network number for type 3 LSAs.
Type 4 – ASBR-Summary LSA – this is needed because Type 5 External LSAs are flooded to all areas and the detailed next-hop information may not be available in those other areas. This is solved by an Area Border Router flooding the information for the router (i.e. the Autonomous System Boundary Router) where the type 5 originated. The link-state ID is the router ID of the described ASBR for type 4 LSAs.
Type 5 – External LSA – these LSAs contain information imported into OSPF from other routing processes. They are flooded to all areas (except stub areas). For “External Type 1” LSAs routing decisions are made by adding the OSPF metric to get to the ASBR and the external metric from there on, while for “External Type 2” LSAs only the external metric is used. The link-state ID of the type 5 LSA is the external network number.
Type 7 – Routers in a Not-so-stubby-area (NSSA) do not receive external LSAs from Area Border Routers, but are allowed to send external routing information for redistribution. They use type 7 LSAs to tell the ABRs about these external routes, which the Area Border Router then translates to type 5 external LSAs and floods as normal to the rest of the OSPF network.