Cisco CCNA Single-Area OSPFv2 Configuration 5 — Questions and Answers
Question 1: An OSPFv2 router advertises a network as O (OSPF intra-area) in the routing table. What does this indicate?
- The route was learned from a different OSPF area
- The route was redistributed from another routing protocol
- The route originated from within the same OSPF area as the receiving router (Correct answer)
- The route is a default route injected by OSPF
Correct answer: The route originated from within the same OSPF area as the receiving router
The 'O' code in the routing table indicates an OSPF intra-area route, meaning the source is in the same area as the router.
Question 2: Which OSPF timer must match between two routers for them to become neighbors?
- SPF delay timer
- LSA retransmit interval
- Dead interval (Correct answer)
- LSA refresh timer
Correct answer: Dead interval
Both the Hello interval and Dead interval must match between OSPF neighbors; mismatched Dead intervals prevent adjacency formation.
Question 3: A router is configured with 'network 0.0.0.0 255.255.255.255 area 0' under 'router ospf 1'. What is the result?
- Only the default route is advertised into OSPF
- All active interfaces on the router participate in OSPF area 0 (Correct answer)
- Only loopback interfaces join OSPF
- The command is rejected as invalid syntax
Correct answer: All active interfaces on the router participate in OSPF area 0
Using 0.0.0.0 with wildcard 255.255.255.255 matches all IP addresses, enabling OSPF on every active interface.
Question 4: What does the 'show ip ospf interface brief' command display?
- A summary of neighbor states on each OSPF interface
- Interface, area, IP address, cost, neighbor count, and DR/BDR information (Correct answer)
- Only interfaces that are currently down in OSPF
- The full OSPF database for each interface
Correct answer: Interface, area, IP address, cost, neighbor count, and DR/BDR information
This command shows a concise table of all OSPF-enabled interfaces with their area, cost, state, and neighbor counts.
Question 5: An administrator wants OSPF to use a specific router ID of 1.1.1.1 without configuring a loopback interface. Which command achieves this?
- ip router-id 1.1.1.1 in global config
- router-id 1.1.1.1 under router ospf (Correct answer)
- ospf router-id 1.1.1.1 in global config
- ip ospf router-id 1.1.1.1 on an interface
Correct answer: router-id 1.1.1.1 under router ospf
The 'router-id' command under 'router ospf' explicitly sets the OSPF router ID to the specified value.
Question 6: Which OSPF network type is automatically assigned to a Cisco serial interface using HDLC or PPP encapsulation?
- Broadcast
- Non-broadcast multi-access (NBMA)
- Point-to-point (Correct answer)
- Point-to-multipoint
Correct answer: Point-to-point
Serial interfaces with HDLC or PPP encapsulation default to OSPF point-to-point network type, with no DR/BDR election.
Question 7: A router running OSPFv2 shows 'Dead interval mismatch' in debug output when attempting to form a neighbor adjacency. Which action resolves this?
- Reload both routers to reset timers to defaults
- Change the Hello interval on one router to match the other
- Configure matching Dead intervals on both routers' connecting interfaces (Correct answer)
- Set OSPF priority to 0 on both interfaces
Correct answer: Configure matching Dead intervals on both routers' connecting interfaces
The Dead interval must match on both sides of the link; use 'ip ospf dead-interval value' on both interfaces to synchronize them.
Cisco CCNA Single-Area OSPFv2 Configuration 5
An OSPFv2 router advertises a network as O (OSPF intra-area) in the routing table.
What does this indicate?