Valid LSA Types for OSPFv2 | CCIE Data Center Exam

Valid LSA Types for OSPFv2

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Question

Which three LSA types are valid for OSPFv2? (Choose three.)

Answers

A. Backbone Summary: an LSA sent by the backbone router to all the OSPF areas.

B. Default LSA: an LSA generated by the ASBR. These LSAs are used to propagate default route into OSP.

C. DR Summary LSA: an LSA sent by the DR router to all the other routers on network.

D. As Internal LSA: an LSA generated by the ASBR. AS Internal LSAs are flooded only within the autonomous system.

E. Router LSA: an LSA sent by every router. This LSA includes the state the cost of all links and a list of all OSPFv2 neighbors on the link.

F. Opaque LSA: an LSA used to extend OSP.

G. Network LSA: an LSA sent by the DR. This LSA lists all routers in the multi-access network.

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Explanations

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A. B. C. D. E. F. G.

EFG.

OSPFv2 (Open Shortest Path First version 2) is a routing protocol used in computer networks to distribute routing information within a single autonomous system (AS). OSPFv2 uses several types of Link State Advertisements (LSAs) to describe the topology of the network. Each LSA type has a specific function and is used for a particular purpose. The question asks which three LSA types are valid for OSPFv2.

The correct answers are:

B. Default LSA: This type of LSA is generated by an Autonomous System Boundary Router (ASBR) and is used to propagate a default route into the OSPFv2 domain. When an OSPFv2 router receives a Default LSA, it installs a default route into its routing table.

D. AS Internal LSA: This type of LSA is generated by an ASBR and is flooded only within the autonomous system. AS Internal LSAs describe routes that are internal to the autonomous system, including routes to networks that are not directly connected to the ASBR.

E. Router LSA: This type of LSA is generated by every router in the OSPFv2 domain. The Router LSA contains information about the router itself, including its ID, its neighbors, and the cost of its links.

The other options are:

A. Backbone Summary: This is not a valid LSA type in OSPFv2.

C. DR Summary LSA: This is not a valid LSA type in OSPFv2. The concept of a DR (Designated Router) only applies to OSPFv2 networks with a multi-access segment.

F. Opaque LSA: This is a valid LSA type in OSPFv2, but it is not one of the three types asked for in the question. Opaque LSAs are used to carry application-specific information, such as traffic engineering parameters.

G. Network LSA: This is a valid LSA type in OSPFv2, but it is not one of the three types asked for in the question. Network LSAs are generated by the DR on a multi-access network and describe the network's topology.

In summary, OSPFv2 uses several types of LSAs to describe the network topology, including Default LSAs, AS Internal LSAs, and Router LSAs. These LSAs are generated by ASBRs and routers within the autonomous system, and they provide routing information that enables the routers to compute the shortest path to each destination network.

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