Module-13 Chapter 1: Single-Area OSPFv2 Configuration

What type of routing protocol is OSPF?

OSPF is a link-state routing protocol.

What protocol did OSPF improve upon?

OSPF was developed as an alternative to RIP.

What are advantages of OSPF over RIP?

Faster convergence and better scalability.

What is a link in OSPF terminology?

An interface on a router or a network segment that connects routers or a stub network.

What is link-state information?

Details including network prefix, prefix length, and cost.

What are the three main OSPF databases?

Adjacency (Neighbor Table), Link-State Database (LSDB), and Forwarding Database (Routing Table).

What command displays the OSPF neighbor table?

show ip ospf neighbor

What command displays the OSPF link-state database?

show ip ospf database

What command displays the OSPF routing table?

show ip route

What algorithm does OSPF use to calculate best paths?

Dijkstra Shortest Path First (SPF) algorithm.

What does the SPF algorithm compute?

The shortest path to each node using cumulative cost.

What is an OSPF area?

A group of routers that share the same LSDB.

What is Area 0 in OSPF?

The backbone area, used in both single-area and multi-area OSPF.

What is the difference between single-area and multiarea OSPF?

Single-area OSPF uses one area (typically area 0); multiarea OSPF uses a hierarchical model with multiple areas.

What is an ABR?

Area Border Router – a router that connects different OSPF areas.

What are benefits of multiarea OSPF?

Smaller routing tables, reduced link-state update overhead, and reduced frequency of SPF calculations.

What is OSPFv3 used for?

For routing IPv6 prefixes.

Does OSPFv3 support both IPv4 and IPv6?

Yes, with OSPFv3 Address Families.

How many packet types does OSPF use?

Five.

Name the five OSPF packet types.

Hello, Database Description (DBD), Link-State Request (LSR), Link-State Update (LSU), Link-State Acknowledgment (LSAck).

What is the purpose of Hello packets?

To discover neighbors and form adjacencies.

What is the purpose of DBD packets?

To summarize and compare OSPF databases between routers.

What is the purpose of LSR packets?

To request missing link-state records.

What is the purpose of LSU packets?

To send the requested link-state records.

What is the purpose of LSAck packets?

To acknowledge receipt of OSPF packets.

What do LSUs contain?

LSAs (Link-State Advertisements).

How many types of LSAs can an LSU packet carry?

Up to 11 different types in OSPFv2.

What is the purpose of LSAs?

To describe the state and cost of each directly connected link.

How are LSAs flooded?

They are sent to all adjacent routers and then flooded to other neighbors.

What happens after receiving LSAs?

Routers build a topology database and run the SPF algorithm.

What happens after the SPF algorithm runs?

Best paths are selected and added to the routing table.

What are the seven OSPF operational states?

Down, Init, Two-Way, ExStart, Exchange, Loading, Full.

What happens in the Down state?

No Hello packets received; router begins sending Hellos.

What happens in the Init state?

Hello packets are received and contain sender’s Router ID.

What is the Two-Way state?

Bi-directional communication is confirmed; DR/BDR election may occur.

What is the ExStart state?

Routers decide who starts sending DBD packets and initial sequence numbers.

What is the Exchange state?

DBD packets are exchanged.

What is the Loading state?

LSRs and LSUs are used to gather additional info.

What is the Full state?

Databases are synchronized; routers are fully adjacent.

What is the All OSPF Routers multicast address?

224.0.0.5

What are DR and BDR?

Designated Router and Backup Designated Router – elected on multiaccess networks to reduce LSA flooding.

What is a DROTHER?

A router on a multiaccess network that is neither DR nor BDR.

What is the purpose of the Dijkstra SPF algorithm in OSPF?

To calculate the shortest path tree and determine the best routes for the routing table.