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?

<p>Type 1 (C)</p> Signup and view all the answers

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

<p>Reduces the number of LSAs processed (D)</p> Signup and view all the answers

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

<p>Backbone Router (BR) (B)</p> Signup and view all the answers

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

<p>Type 4 and 5 (B)</p> Signup and view all the answers

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

<p>Type 3 (D)</p> Signup and view all the answers

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

<p>Advertises link-local addresses to neighboring routers (C)</p> Signup and view all the answers

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

<p>It remains within the specific OSPF area (D)</p> Signup and view all the answers

What is the primary purpose of an OSPF Virtual Link?

<p>To establish adjacency when direct connectivity to Area 0 is not possible (C)</p> Signup and view all the answers

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

<p>By providing a logical connection to the backbone (A)</p> Signup and view all the answers

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

<p>area 1 virtual-link 3.3.3.3 (D)</p> Signup and view all the answers

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

<p>Advertise IPv6 prefixes for a specific OSPF area (C)</p> Signup and view all the answers

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

<p>To replace Type 3, 4, and 5 LSAs used in IPv4 (A)</p> Signup and view all the answers

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

<p>area 1 virtual-link 1.1.1.1 (B)</p> Signup and view all the answers

Flashcards

Internal Router

A router located within a single OSPF area, handling intra-area communication.

Area Border Router (ABR)

A router that connects multiple OSPF areas to the backbone area (Area 0), summarizing inter-area routes and propagating them.

Backbone Router (BR)

A router located in the backbone area (Area 0), responsible for handling inter-area and external connectivity.

Autonomous System Boundary Router (ASBR)

A router that connects to external networks or different routing domains, advertising external routes to the OSPF network.

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What does LSA Type 1 advertise?

Type 1 LSAs advertise information within an area about the router itself and directly connected networks.

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What does LSA Type 2 advertise?

Type 2 LSAs provide information about networks within the same area, including the cost to reach them.

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What does LSA Type 3 advertise?

Type 3 LSAs summarize inter-area routes for a specific area, allowing ABRs to propagate information about other areas.

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What does LSA Type 4 advertise?

Type 4 LSAs advertise external routes learned from other routing domains, helping ASBRs to propagate this information.

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Type 8 LSA: Link-LSA

This LSA advertises IPv6 link-local addresses and network information to neighboring routers on the same link. It ensures that all routers on a link share the same IPv6 prefix and link-local addresses.

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Type 9 LSA: Intra-Area-Prefix LSA

This LSA advertises IPv6 prefixes for a specific OSPF area (a group of routers) or a specific network within that area. It provides the vital routing information for OSPFv3, replacing older LSAs used in IPv4 OSPF.

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OSPF Virtual Link: Concept

A virtual link is a logical connection in OSPF that allows two routers to communicate even when they don't have a direct physical connection.

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Purpose 1: Connecting Disjointed Area 0 Segments

The primary purpose of an OSPF virtual link is to connect separate sections of Area 0, the OSPF backbone area, ensuring that all routers remain part of the OSPF network.

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Purpose 2: Connecting Non-Backbone Areas

Virtual links allow non-backbone OSPF areas (areas other than Area 0) to connect to the backbone, enabling them to exchange routing information and become transit areas for other areas.

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Virtual Link Configuration

Virtual links are configured on both routers involved in the connection. Each router defines the virtual link with the router ID of the other router.

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OSPF Router ID: Concept

Router IDs are used to identify individual routers within an OSPF network. They are typically assigned by the administrator and can be chosen using different methods.

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Virtual Link Configuration: Router IDs

When configuring a virtual link, each router specifies the router ID of the other router involved in the virtual connection. This allows them to establish a connection and exchange routing information.

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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.
  • 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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2020 Paper PDF - OSPF Routing

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.

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