Cisco CCNA Single-Area OSPFv2 Configuration 3 — Questions and Answers
Question 1: A router shows 'OSPF: Hello from 192.168.1.2 with mismatched area ID'. What is the most likely cause?
- The neighbor has a different router ID
- One interface is in area 0 and the other is in a different area (Correct answer)
- The Hello interval is different on each router
- The subnet masks do not match
Correct answer: One interface is in area 0 and the other is in a different area
An area ID mismatch means the two interfaces are configured in different OSPF areas, preventing adjacency.
Question 2: What is the purpose of the OSPF DR (Designated Router) on a broadcast network?
- To assign IP addresses to other routers
- To reduce LSA flooding by acting as a central point for LSDB synchronization (Correct answer)
- To perform route summarization for the area
- To authenticate all OSPF packets in the segment
Correct answer: To reduce LSA flooding by acting as a central point for LSDB synchronization
The DR reduces OSPF traffic on multi-access segments by collecting and distributing LSAs on behalf of all routers.
Question 3: Which OSPF state indicates that two routers have fully synchronized their Link State Databases?
- 2-Way
- ExStart
- Exchange
- Full (Correct answer)
Correct answer: Full
The Full state means both routers have identical LSDBs and the adjacency is complete.
Question 4: A Cisco router has 'passive-interface GigabitEthernet0/1' configured under OSPF. What is the effect?
- OSPF is disabled on Gi0/1 entirely
- Gi0/1 still advertises its network but does not send or receive Hello packets (Correct answer)
- Gi0/1 sends Hellos but does not form adjacencies
- OSPF routes learned via Gi0/1 are suppressed
Correct answer: Gi0/1 still advertises its network but does not send or receive Hello packets
A passive interface suppresses Hello packets so no adjacencies form, but the network is still advertised into OSPF.
Question 5: What is the OSPF cost of an interface with a bandwidth of 100 Mbps using the default reference bandwidth?
- 1 (Correct answer)
- 10
- 100
- 1000
Correct answer: 1
OSPF cost = reference bandwidth (100 Mbps) / interface bandwidth (100 Mbps) = 1.
Question 6: A network admin wants to change the OSPF reference bandwidth to accommodate Gigabit links. Which command accomplishes this?
- ip ospf cost 1000 under each interface
- bandwidth 1000 under each interface
- auto-cost reference-bandwidth 1000 under router ospf (Correct answer)
- ospf reference-bandwidth 1000 in global config
Correct answer: auto-cost reference-bandwidth 1000 under router ospf
The 'auto-cost reference-bandwidth 1000' command under 'router ospf' sets the reference to 1000 Mbps, giving GigE a cost of 1.
Question 7: Which show command displays the OSPF router ID, process ID, area information, and SPF statistics?
- show ip ospf neighbor detail
- show ip ospf (Correct answer)
- show ip protocols
- show ip ospf database
Correct answer: show ip ospf
The 'show ip ospf' command provides process-level details including router ID, area assignments, and SPF run statistics.
Cisco CCNA Single-Area OSPFv2 Configuration 3
A router shows 'OSPF: Hello from 192.168.1.2 with mismatched area ID'.
What is the most likely cause?