Course 9: OSPF·Lesson 3.2 (6 of 6 in this course)·75 of 104 in the CCNA series
Test: OSPF
Ten questions on the whole course, each with an explanation.
Intermediate · 10 min read
After this lesson, you can check that you can predict OSPF neighbour states, elections, costs and routes on a small network.
OSPF (Open Shortest Path First) is a link-state interior routing protocol. Routers form neighbourships, flood link-state advertisements so that every router in an area holds the same database, and each router runs the SPF algorithm to find the lowest-cost path to every network.
In simple terms: Routers share a map of the network with each other, and each one works out its own shortest way to every destination.
Ten questions on the whole course, using the lab network: R1, R2 and R3 in a line with LANs 192.168.1.0/24, 192.168.2.0/24 and 192.168.3.0/24, and a reference bandwidth of 10 000 Mbps. If you get one wrong, the explanation names the lesson to go back to.
Predict · scenario 1
1. Which of these does NOT have to match for two routers to become OSPF neighbours on a link?
Predict · scenario 2
2. R2 shows R3 in the 2WAY/DROTHER state on a LAN where R1 is the DR and R4 the BDR. Is something wrong?
Predict · scenario 3
3. Four routers on a LAN all have priority 1. One router has priority 0. Which can become DR?
Predict · scenario 4
4. A router has no router-id command, a loopback 10.0.0.1 and interfaces 192.168.5.1 and 172.31.0.1. What is its router ID?
Predict · scenario 5
5. R2 has network 10.0.0.0 0.255.255.255 area 0. Which interfaces does that enable?
Predict · scenario 6
6. R2's LAN interface is passive. Can PCs on LAN 3 still reach LAN 2?
Predict · scenario 7
7. With a reference bandwidth of 10 000 Mbps, what does R1 show as the cost to LAN 3 (three gigabit hops)?
Predict · scenario 8
8. R3 shows O*E2 0.0.0.0/0 [110/1]. Where did it come from?
Predict · scenario 9
9. Two neighbours are stuck in EXSTART. Hellos, area and timers match. What is the likely cause?
Predict · scenario 10
10. All neighbours are Full, but R1 routes to 192.168.3.0/24 with S, not O. Why?