ICND1 OSPF Configuration 5 — Questions and Answers
Question 1: Which statement correctly describes OSPF route summarization at an Area Border Router (ABR)?
- Summarization is automatic between all OSPF areas
- The 'area range' command is used on ABRs to summarize routes between areas (Correct answer)
- The 'summary-address' command is used on ABRs for inter-area summarization
- OSPF does not support route summarization
Correct answer: The 'area range' command is used on ABRs to summarize routes between areas
The 'area range' command on an ABR aggregates Type 3 LSAs sent between areas, reducing LSDB size.
Question 2: A router's OSPF neighbor is stuck in the EXSTART state. What is the most likely cause?
- Mismatched area IDs
- MTU mismatch between the two routers (Correct answer)
- Mismatched hello timers
- The remote router has priority 0
Correct answer: MTU mismatch between the two routers
An MTU mismatch causes DBD packets to be dropped, stalling the adjacency in the ExStart/Exchange state.
Question 3: Which command manually sets the OSPF cost on an interface to 50?
- router ospf cost 50
- ospf cost 50
- ip ospf cost 50 (Correct answer)
- bandwidth 50
Correct answer: ip ospf cost 50
The interface-level command 'ip ospf cost 50' directly overrides the automatically calculated OSPF cost.
Question 4: What does the 'network 10.0.0.0 0.255.255.255 area 0' command do under the OSPF process?
- Adds a static route for 10.0.0.0/8 in area 0
- Enables OSPF on all interfaces with IPs matching the 10.x.x.x range and places them in area 0 (Correct answer)
- Summarizes the 10.0.0.0/8 network for area 0
- Blocks OSPF on interfaces outside the 10.0.0.0 range
Correct answer: Enables OSPF on all interfaces with IPs matching the 10.x.x.x range and places them in area 0
The 'network' command with a wildcard mask enables OSPF on matching interfaces and assigns them to the specified area.
Question 5: Which OSPF packet type is sent to request specific LSAs that a router does not have in its LSDB?
- Database Description (DBD)
- Link-State Update (LSU)
- Link-State Request (LSR) (Correct answer)
- Hello
Correct answer: Link-State Request (LSR)
LSR packets are sent after comparing DBDs to request specific LSAs that are missing from the local LSDB.
Question 6: What is the default OSPF process ID scope on a Cisco router?
- The process ID must match between OSPF neighbors
- The process ID is locally significant and does not need to match neighbors (Correct answer)
- The process ID must be between 1 and 65535 and must match across the area
- The process ID is globally significant across the entire OSPF domain
Correct answer: The process ID is locally significant and does not need to match neighbors
The OSPF process ID is locally significant only; different routers can use different process IDs and still form adjacencies.
Question 7: Which show command confirms that OSPF routes have been installed in the routing table and displays their costs?
- show ip ospf database
- show ip ospf neighbor
- show ip route ospf (Correct answer)
- show ip ospf topology
Correct answer: show ip route ospf
'show ip route ospf' displays all OSPF-learned routes with their metric (cost) and next-hop information.
ICND1 OSPF Configuration 5
Which statement correctly describes OSPF route summarization at an Area Border Router (ABR)?