OSPF-1

Question 1

What is the OSPF Routing Protocol?

• Is OSPF a Link State or path-vector routing protocol?
• How does it calculate the shortest paths?
• What is the AD?
• What is the metric?
• What is the Transport?
• What are the IPs for OSPF multicast?

Answer 1

• OSPF is an Link State routing protocol.
• OSPF uses the Dijkstra algorithm to construct the shortest paths.
• OSPF AD: 110
• OSPF Metric: Cost (Bandwidth)
• OSPF Transport: IP/89
• OSPF Multicast: 224.0.0.5 & 224.0.0.6

Question 2

What are the steps required to change neighborship into adjacency?

Answer 2

1. Two-way communication (using Hello Protocol).
2. Database Synchronization, which means the exchange of Database Description (DD) packets, Link State Request (LSR) packets, Link State Update (LSU) packets.

After Database synchronization is complete, the two routers are considered adjacent.

Question 3

Explain LSA (Link-State Advertisement), LSU (Link State Update), and LSR (Link State Request).

Answer 3

• LSAs (Link-State Advertisements): Are used to exchange routing and topology information.
• LSR (Link State Request): Each router then checks its topology database and sends Link State Request (LSR) message requesting all LSAs that were not found in its topology table.
• LSU (Link State Update): Other router responds with the Link State Update (LSU) that contains all LSAs requested by the neighbor.

Question 4

Explain OSPF Router ID?

Answer 4

The Router ID is used to identify the Router.

• The OSPF Router ID can be manually set.
• The OSPF Router ID can be The highest IP address of the router’s loopback interfaces.
• If no loopback is present, then the highest IP address of the router’s physical interfaces will be chosen as the Router ID.

R1(config)# router ospf 5
R1(config-router)# router-id 5.5.5.5

Question 5

What is the difference between an OSPF neighbor and an adjacent neighbor?

Answer 5

LSAs are exchanged only among adjacent routers, not among neighbor routers.