The OSPF hello timer has been set to 15 seconds on a router in a point-to-point network. By default,
what is the dead interval on this router? - 60 seconds - By default, the dead interval is calculated as 4
times the hello interval.
At which OSPF state are neighbor routers converged and able to exchange routing updates? - Full
What 3 databases does OSPF create and keep in RAM? - 1. Adjacency - neighbor table
2. Link-state (LSDB) - topology table
3. Forwarding - routing table
What does the OSPF Adjacency database contain? - A Neighbor table that lists all neighbor routers - can
be viewed using the show ip ospf neighbor command. The neighbor table is unique for each router.
What does the OSPF LSDB contain? - A topology table lists the network topology, info about all other
routers on the network. All routers within an area have identical LSDB. Can be viewed using the show ip
ospf database command.
What does the OSPF Forwarding Database contain? - A routing table lists the routes generated when an
algorithm is run. Each router's table is unique & contains info on how and where to send packets. Can be
viewed using the show ip route command.
, OSPF routers exchange messages to discover neighboring routers. Name the 5 packets used to exchange
messages: -
What is the Dijkstra SPF algorithm based on? - the cumulative cost from one router to reach a
destination
How does Dijkstra's algorithm work? - 1. places each router at root of SPF tree and calculates the
shortest path to each node
2. SPF tree calculates the best routes
3. OSPF places best routes in forwarding database to make the routing table
To reach a state of convergence, what 4 steps does OSPF complete? - 1. Establish Neighbor Adjacencies -
hello packets are sent out all OSPF-enabled interfaces
2. Exchange Link-State Advertisements (LSAs) - routers flood LSAs to adjacent routers which contain the
state, cost, and sequence # of each directly connected link
3. Build the Topology Table - based on the LSAs a router receives - eventually holds all info about
networks topology
4. Execute the SPF Algorithm - which then creates the SPF tree
What is an OSPF area? - A group of routers that share the same link-state info in their LSDBs.
What is a Single-area OSPF? - Used in a small network - all routers are within area 0 aka the backbone
area.
A Multi-area OSPF is used in larger networks to dived a large AS (autonomous system) into smaller
areas. What are 3 characteristics of a multi-area OSPF? - 1. it lightens the load on routers 2. all areas
must connect to the backbone (0) area 3. interconnecting routers are called Area Border Routers (ABRs).
What are 4 advantages of Multi-area OSPFs? - 1. smaller routing tables because network addresses can
be summarized between areas
2. reduced link-state update overhead - uses less processing and memory
3. reduced frequency of SPF calculation -
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