Juniper Networks OSPF Router: Suppressing LSA Types in Area 1

Suppressing LSA Types in Area 1

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Question

Router A is an OSPF router connected to both Area 0 and Area 1 Area 1 has been configured as a stub area Which two LSA types does Router A suppress from

Area 1?

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Explanations

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A. B. C. D.

BD

In an OSPF network, routers exchange information about the network topology using Link State Advertisements (LSAs). When an area is configured as a stub area, some of the LSAs are suppressed to reduce the size of the routing table and improve network performance.

In this scenario, Router A is an OSPF router that is connected to both Area 0 (the backbone area) and Area 1, which has been configured as a stub area. The question asks which two LSA types are suppressed from Area 1.

There are seven types of LSAs in OSPF, but not all of them are used in every area. The LSAs that are suppressed in a stub area are:

  1. Type 4 Summary ASBR LSA: This LSA advertises the ASBR (Autonomous System Boundary Router) summary information, which is used to route traffic between OSPF and non-OSPF networks. In a stub area, this information is not needed because there are no external routes allowed, so the Type 4 LSA is suppressed.

  2. Type 5 External LSA: This LSA advertises routes from outside the OSPF domain, such as routes learned from other routing protocols or static routes. In a stub area, external routes are not allowed, so the Type 5 LSA is also suppressed.

The LSAs that are not suppressed in a stub area are:

  1. Type 1 Router LSA: This LSA advertises information about the router itself, such as its interfaces, neighbors, and link state.

  2. Type 2 Network LSA: This LSA advertises information about broadcast and non-broadcast networks, including the routers and links connected to the network.

  3. Type 3 Summary LSA: This LSA advertises the summary information for networks in other areas, which allows routers in the stub area to route traffic to those networks via the backbone.

  4. Type 7 NSSA External LSA: This LSA is used in a stub area that is configured as a not-so-stubby area (NSSA). It advertises external routes that have been translated into OSPF routes by an NSSA ASBR.

Therefore, the two LSA types that Router A suppresses from Area 1, which is configured as a stub area, are:

B. External LSA (Type 5) D. ASBR Summary LSA (Type 4)

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