OSPF Practice Questions

Answers and explanations appear when you work through the set above.

1. Under router ospf configuration mode, what does the network 0.0.0.0 255.255.255.255 area 0 statement do?

   • Disables OSPF entirely
   • Enables OSPF area 0 on all IP-addressed interfaces
   • Advertises only a default route
   • Restricts OSPF area 0 to the router's loopback interfaces

2. Why mark an OSPF-enabled user LAN interface as passive when its subnet should be advertised but no OSPF neighbors should form there?

   • Passive mode disables IP forwarding on that interface
   • Suppresses Hellos while advertising the connected subnet
   • It removes the loopback's subnet from the routing table
   • It forces the loopback to become the DR

3. A Cisco IOS router already has a usable IPv4 default route in its routing table. Which OSPF process command advertises that default into a normal, non-stub OSPF area?

   • default-information originate
   • redistribute static
   • network 0.0.0.0 0.0.0.0 area 0
   • ip default-network

4. In show ip route output, a route learned via OSPF is marked with which code?

   • D (EIGRP)
   • R (RIP)
   • O
   • S (static)

5. A router that originates a default route into OSPF, and whose routing table also shows external routes injected by another router, is best described as what OSPF role?

   • Backbone router only
   • ASBR (external-route originator)
   • ABR (router connecting multiple OSPF areas)
   • Designated Router (DR)

6. Which command lists each OSPF neighbor's router ID, state, and the interface the adjacency was formed over?

   • show ip ospf database
   • show ip ospf neighbor
   • show ip protocols
   • show ip ospf interface

7. An OSPF broadcast segment contains exactly two routers. They discover each other but remain 2-WAY, with neither a DR nor BDR elected. Which condition explains this?

   • A mismatched OSPF process number between the two routers
   • Both have priority 0, excluding them from DR/BDR election
   • The routers have different router IDs
   • OSPF is disabled on the loopback interfaces

8. By default, what value determines a router's OSPF router ID if no loopback interface and no manually configured router-id exist?

   • The lowest MAC address on the router
   • Highest IPv4 on an up/up physical port
   • A randomly generated 32-bit value
   • The router hostname encoded as a 32-bit IPv4-like value

9. Which command displays a router's OSPF process ID, router ID, configured networks with their areas, and administrative distance in one summary?

   • show ip ospf database
   • show ip protocols
   • show ip ospf border-routers
   • show running-config | section ospf

10. On a point-to-point serial link running OSPF, what happens to the DR/BDR election process compared to an Ethernet segment?

    • It works exactly the same as on Ethernet
    • Point-to-point OSPF does not elect a DR or BDR
    • Only a BDR is elected, never a DR
    • The election is based on interface bandwidth instead of priority

11. What does the OSPF cost of an interface default to being based on, unless manually overridden?

    • Reference bandwidth divided by interface bandwidth
    • Hop count along the shortest route to the destination subnet
    • The interface's MTU
    • A fixed value of 1 for every interface type

12. A router shows two equal-cost paths to the same destination network via OSPF in its routing table. What does this reflect?

    • A routing loop
    • Equal-cost multipath (ECMP) load balancing
    • A misconfiguration that should be fixed
    • A redistribution error

13. Which OSPF LSA type describes a router's own directly connected links and is originated by every OSPF-speaking router?

    • Type 1, Router LSA
    • Type 2, Network LSA
    • Type 3, Summary LSA
    • Type 5, External LSA

14. An OSPF neighbor relationship fails to form and the console shows a mismatched Hello or Dead interval. What must match between two OSPF neighbors for an adjacency to succeed?

    • Area and router ID, with Hello and Dead timers negotiated after discovery
    • Hello/Dead timers, area, and authentication settings
    • Router ID and process number, with authentication negotiated automatically
    • Only the process number

15. Which command displays per-interface OSPF network type, cost, timers, and DR/BDR details where applicable?

    • show ip ospf interface <name>
    • show ip ospf neighbor detail
    • show cdp neighbors detail
    • show ip ospf virtual-links

16. Why does OSPF require every non-backbone area to connect to area 0, either directly or through a virtual link?

    • It is only a Cisco best practice, not a protocol requirement
    • Inter-area routing transits area 0, the backbone
    • Area 0 is required only when using authentication
    • Non-backbone areas can only run RIP instead

17. In show ip ospf database output, what does the 'Net Link States' section (Type 2 LSAs) represent?

    • Static routes redistributed into OSPF by an autonomous system boundary router
    • Router-to-router point-to-point links
    • DR-originated descriptions of multi-access segments and attached routers
    • External routes learned from BGP

18. R1 and R2 share an Ethernet link and their OSPF adjacency is stuck in EXSTART. An AI assistant recommends changing R2's router ID because it suspects a duplicate. show interfaces reports MTU 1500 on R1's link and MTU 1400 on R2's. How should you treat the recommendation?

    • Apply it, because a duplicate router ID is the usual cause of an EXSTART loop
    • Reject it, because the output points to an MTU mismatch: align the MTU on both ends
    • Apply it, then clear the OSPF process on both routers to force a new election
    • Reject it, and move R2's interface into a different OSPF area instead

19. On a broadcast segment with four routers, show ip ospf neighbor on R3 lists neighbor 4.4.4.4 in state 2WAY/DROTHER. An AI assistant flags this as a failed adjacency and recommends restarting OSPF on R3. R3 is itself a DROTHER. What is the most accurate evaluation?

    • The recommendation is correct, because every OSPF neighbor must reach FULL
    • The recommendation is correct, but the reset should be done on the DR instead
    • Reject: DROTHER peers stay 2WAY and form FULL adjacencies with the DR and BDR
    • The recommendation is wrong: 2WAY means the hello timers differ and must be matched