2020 Paper - OSPF Router Types and LSA Usage

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Questions and Answers

Which router type connects multiple areas to the backbone area in a multi-area OSPF hierarchical network?

Autonomous System Boundary Router (ASBR)

Internal Router (IR)

Backbone Router (BR)

Area Border Router (ABR) (correct)

What is the primary function of the Link State Advertisement (LSA) Type 3 in OSPF?

Summarize and propagate inter-area routes (correct)

Advertise external routes

Advertise intra-area routes

Connect to external networks

What is the effect of making Area 51 a Totally Stubby Area in OSPF?

Blocks Type 1 LSAs only

Expands the routing table size

Blocks both external and inter-area routes (correct)

Injects multiple default routes

Which LSA type is primarily used by Internal Routers for intra-area communication?

Type 1 Signup and view all the answers

What is one of the main advantages of configuring Area 51 as a Totally Stubby Area?

Reduces the number of LSAs processed Signup and view all the answers

What type of router ensures inter-area and external connectivity by processing all LSA types?

Backbone Router (BR) Signup and view all the answers

Which LSA types do ASBRs use to advertise external routes in OSPF?

Type 4 and 5 Signup and view all the answers

Which LSA type is used by ABRs to summarize routes from multiple areas?

Type 3 Signup and view all the answers

What is the primary function of Type 8 Link-LSA?

Advertises link-local addresses to neighboring routers Signup and view all the answers

Which of the following statements accurately describes the scope of Type 9 Intra-Area-Prefix LSA?

It remains within the specific OSPF area Signup and view all the answers

What is the primary purpose of an OSPF Virtual Link?

To establish adjacency when direct connectivity to Area 0 is not possible Signup and view all the answers

How does an OSPF Virtual Link connect disjointed Area 0 segments?

By providing a logical connection to the backbone Signup and view all the answers

What command should be used on Router R1 to establish a virtual link to Router R3?

area 1 virtual-link 3.3.3.3 Signup and view all the answers

Which OSPF area functionality is specifically addressed by Type 9 LSAs?

Advertise IPv6 prefixes for a specific OSPF area Signup and view all the answers

What is not a key use of Type 8 Link-LSA?

To replace Type 3, 4, and 5 LSAs used in IPv4 Signup and view all the answers

What command is necessary for Router R3 to create a virtual link to Router R1?

area 1 virtual-link 1.1.1.1 Signup and view all the answers

Study Notes

2020 Paper - Question 3 (a)

Router Types in Multi-Area OSPF:
- Backbone Router (BR): Located in Area 0 (backbone).
- Area Border Router (ABR): Connects multiple areas to the backbone.
- Internal Router (IR): Located within a single area.
- Autonomous System Boundary Router (ASBR): Connects to external networks or different routing domains.

2020 Paper - Question 3 (a)(ii)

LSA Usage by Router Types:
- Internal Routers (IRs): Use LSA types 1 and 2 for intra-area communication.
- Area Border Routers (ABRs): Summarize and propagate inter-area routes using LSA types 1, 2, and 3.
- Autonomous System Boundary Routers (ASBRs): Advertise external routes using LSA types 4 and 5.
- Backbone Routers (BRs): Ensure inter-area and external connectivity by processing all LSA types.

2020 Paper - Question 3 (iv)(A)

Effect of Making Area 51 a Totally Stubby Area:
- Blocks External and Inter-Area Routes: Completely blocks external routes (Type 5 LSAs) and inter-area routes (Type 3 LSAs).
- Minimal Routing Table: Routers in Area 51 only store intra-area routes (Type 1 LSAs) and a single default route for all other traffic.
- Improved Scalability and Performance: Reduces the size of the routing table, saving memory and CPU resources. Optimal for small areas not needing detailed inter-area or external routing.

2020 Paper - Question 3 (iv)(B)

New LSA Types in IPv6 Implementations:
- Type 8 (Link-LSA): Advertises IPv6 link-local addresses and associated network information on the same link.
- Type 9 (Intra-Area-Prefix LSA): Advertises IPv6 prefixes for a specific OSPF area. Replaces Type 3, 4, and 5 LSAs in IPv4 OSPF for IPv6 routing.

2020 Paper - IPv6 Implementation and OSPF Virtual Link Concepts.

OSPF Virtual Link: A logical connection used to establish OSPF adjacency between routers where direct connectivity to the backbone area (Area 0) isn't possible.
Purpose of OSPF Virtual Link:
- Connects disjointed Area 0 segments.
- Provides Backbone connectivity to non-backbone areas. Allows an area to function as a transit area for connecting other areas to Area 0.

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Description

Test your knowledge on the types of routers used in Multi-Area OSPF and their corresponding LSA usages. This quiz covers Backbone Routers, Area Border Routers, Internal Routers, and Autonomous System Boundary Routers, as well as the effects of configuring areas as totally stubby. Ideal for students familiar with OSPF concepts.