ICND1 OSPF Configuration 4 — Questions and Answers
Question 1: Which command sets the OSPF reference bandwidth to 1000 Mbps to correctly calculate costs for Gigabit interfaces?
- ip ospf cost 1000
- auto-cost reference-bandwidth 1000 (Correct answer)
- ip ospf bandwidth 1000
- ospf reference-bandwidth 1000000
Correct answer: auto-cost reference-bandwidth 1000
'auto-cost reference-bandwidth 1000' under the OSPF process sets the reference to 1000 Mbps, giving GigE interfaces a cost of 1.
Question 2: What is the multicast address used by OSPF Designated Routers and Backup Designated Routers?
- 224.0.0.5
- 224.0.0.6 (Correct answer)
- 224.0.0.1
- 224.0.0.10
Correct answer: 224.0.0.6
224.0.0.6 is the AllDRouters multicast address used to send updates specifically to the DR and BDR.
Question 3: A network engineer needs to advertise a default route into OSPF. Which command accomplishes this?
- network 0.0.0.0 0.0.0.0 area 0
- default-information originate (Correct answer)
- ip ospf default-route
- redistribute default-route ospf
Correct answer: default-information originate
'default-information originate' under the OSPF process redistributes a default route into the OSPF domain.
Question 4: Which OSPF neighbor state indicates that routers have exchanged DBD packets and are now requesting missing LSAs?
- Exchange
- ExStart
- Loading (Correct answer)
- Full
Correct answer: Loading
In the Loading state, routers send LSR packets to request specific LSAs that were identified as missing during Exchange.
Question 5: What is the effect of configuring 'ip ospf priority 0' on an interface?
- The router becomes the DR automatically
- The router is ineligible to become the DR or BDR (Correct answer)
- The router's OSPF cost is set to zero
- The interface is excluded from OSPF area 0
Correct answer: The router is ineligible to become the DR or BDR
An OSPF priority of 0 makes the router ineligible to become either the Designated Router or Backup Designated Router.
Question 6: Which command verifies that OSPF is enabled on a specific interface and shows its cost?
- show ip ospf neighbor detail
- show ip route ospf
- show ip ospf interface brief (Correct answer)
- show ip protocols
Correct answer: show ip ospf interface brief
'show ip ospf interface brief' lists all OSPF-enabled interfaces with their area, IP, cost, state, and neighbor counts.
Question 7: OSPF uses which algorithm to calculate the shortest path to each destination?
- Bellman-Ford
- Diffusing Update Algorithm (DUAL)
- Dijkstra's Shortest Path First (SPF) (Correct answer)
- Distance Vector with split horizon
Correct answer: Dijkstra's Shortest Path First (SPF)
OSPF uses Dijkstra's SPF algorithm to compute loop-free shortest paths based on cumulative link costs.
ICND1 OSPF Configuration 4
Which command sets the OSPF reference bandwidth to 1000 Mbps to correctly calculate costs for Gigabit interfaces?