Twenty-five 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. R1 alone connects to the lab ISP and originates the default in normal area 0. Questions about a shared LAN use their own stated routers and election roles; they are separate from the three-router chain.
Choose the answer supported by the evidence, then explain why the other options do not fit. There is no timer. You can retry after reading the feedback. Review the reference sheet or the troubleshooting lesson when a term is unfamiliar.
1. On an ordinary broadcast IPv4 Ethernet subnet, which value does NOT have to match for two routers to become OSPF neighbours?
2. R2 shows R3 in the 2WAY/DROTHER state on a LAN where R1 is the DR and R4 the BDR. Is something wrong?
3. Five routers share a LAN: four have priority 1 and one has priority 0. Which are eligible to become the designated router (DR)?
4. When OSPF starts, a router has no router-id command, an up loopback 10.0.0.1 and up interfaces 192.168.5.1 and 172.31.0.1. Which router ID does classic IOS select?
5. R2 has network 10.0.0.0 0.255.255.255 area 0. Which interfaces does that enable?
6. R2's up LAN interface is selected for OSPF and passive. With healthy transit links, host gateways and return routes, can PCs on LAN 3 reach LAN 2?
7. With a reference bandwidth of 10 000 Mbps, what does R1 show as the cost to LAN 3 (three gigabit hops)?
8. R3 shows O*E2 0.0.0.0/0 [110/1]. Where did it come from?
9. Two neighbours are stuck in EXSTART. Hellos, area and timers match. What is the likely cause?
10. All neighbours are Full. R1 has an eligible OSPF route and an installed static route with distance 1 to the same 192.168.3.0/24 prefix. Why does the route show S?
11. Which OSPF packet type does a router send when it wants a full copy of an LSA it saw listed in a DBD?
12. In ExStart, R1 (1.1.1.1) and R2 (2.2.2.2) both claim to be master. Who wins?
13. The DR on a LAN has been declared lost, and a healthy backup designated router (BDR) is present. Which describes the role change?
14. In normal multicast flooding on a broadcast LAN, a DROther sends a new LSA update towards the elected routers. Which destination does it use?
15. R2 has passive-interface default and no other passive commands. What happens to its neighbours?
16. R1 is the only default originator in normal area 0. It uses plain default-information originate without always or a route-map, and now has no installed default. What remains after withdrawal converges?
17. In this normal-area lab, which LSA type carries the external default from default-information originate?
18. With the default reference bandwidth, what is the cost of a 1 Gbps and of a 100 Mbps interface?
19. An interface has ip ospf cost 50 and bandwidth 10000 (kbps). The reference is 100 Mbps. What is its cost?
20. Which router creates a type 2 (network) LSA?
21. A routing table shows O IA 10.5.0.0/16. What does IA tell you?
22. R3's Loopback1 is 172.16.3.1/24 in OSPF with default settings. What do other routers learn?
23. One end of a link uses the broadcast type, the other non-broadcast, timers at default. Result?
24. R2's LAN interface shows a neighbour with router ID 10.10.10.10 that nobody configured. What was missed?
25. The three outgoing gigabit interfaces should each cost 10, with no manual overrides. R3 instead sees LAN 1 at cost 21. R1 and R3 use reference 10 000 Mbps. Which R2 setting could explain the difference?
Turn a missed answer into a lab check
For a neighbour question, compare show ip ospf interface and show ip ospf neighbor. For a route question, inspect the relevant record with show ip ospf database, then the destination with show ip route. Write the evidence you expect before running the command. Use the isolated three-router lab for deliberate faults and restore one change before introducing another.