27. Explain why OSPF is better than RIP in a large internetwork.

• Fast convergence
  Only the routing changes (not the entire routing table) are flooded rapidly to other routers.
• VLSM support
• No reachability limitation
  Multicasts minimally sized LS updates and sends them only when a change occurs.
• Optimal route selection
  Computes cost based on the interfaces bandwidth setting, so not limited to a hop count metric.
• Area grouping
  By dividing its communication within areas, it limits traffic regionally to prevent changes in one area from impacting performance in other areas.
• Exchanges link information upon initial discovery of changes using LSA packets instead of broadcast RT periodically.
• Designed for large (more than 50 routers) scalable growing internetworks.
• Maintain a common picture of the network.

28. Explain how OSPF discovers, chooses, and maintains routes.

1. Init
   Interface detected a hello packet coming from a neighbor but bi-directional communication has not yet been established.
2. Two-way
   Bi-directional communication exists with a neighbor and the router has seen itself in the hello packets coming from a neighbor.
3. Exstart
   Routers establish a master / slave relationship and determine the initial Database Description (DBD) sequence number.
4. Exchange
   Routers send Database Description Packets (DDP) describing its entire link state database to neighbors.
5. Loading
   Router will send Link State Request packets to neighbors requesting more recent LSA's than have been discovered.
6. Full
   The neighboring routers are adjacent, and will have a similar link-state database.

29. Configure OSPF for proper operation.

30. Verify OSPF operation.