CCNAv7 Module 2 Quiz - Single-Area OSPFv2 Configuration Answers

1. Which criterion is preferred by the router to choose a router ID?

the IP address of the highest configured loopback interface on the router
the IP address of the highest active OSPF-enabled interface
the router-id rid command
the IP address of the highest active interface on the router

Explanation: The preferred order of criteria for Cisco routers to identify the router ID is: an explicitly configured router using the router-id rid command; the IP address of any configured loopback interface; and the IP address of any active interface on the router (it does not have to be an OSPF-enabled interface).

2. Which wildcard mask would be used to advertise the 192.168.5.96/27 network as part of an OSPF configuration?

0.0.0.32
0.0.0.31
255.255.255.224
255.255.255.223

Explanation: The wildcard mask can be found by subtracting the subnet mask from 255.255.255.255.

3. The following three networks are directly connected to an OSPF router; 192.168.0.0/24, 192.168.1.0/24, and 192.168.2.0/24. Which OSPF network command would advertise only the 192.168.1.0 network to neighbors?

router(config-router)# network 192.168.1.0 0.0.0.0 area 0
router(config-router)# network 192.168.1.0 0.0.0.255 area 0
router(config-router)# network 192.168.1.0 255.255.255.255 area 0
router(config-router)# network 192.168.0.0 0.0.15.255 area 0

Explanation: To advertise only the 192.168.1.0/24 network the wildcard mask used in the network command must match the first 24-bits exactly. To match bits exactly, a wildcard mask uses a binary zero. This means that the first 24-bits of the wildcard mask must be zero. The low order 8-bits can all be set to 1.

4. Which three parameters should match in order for a pair of routers to form an adjacency when running OSPFv2? (Choose three.)

OSPFv2 process number
OSPFv2 type of network
router ID
interface priority
hello timer
subnet mask

Explanation: For a couple of routers that are running OSPFv2 to form an adjacency, the following parameters must match: subnet mask, network type, hello and dead timers, a corresponding network command, and the authentication information.

5. What are two features of the OSPF routing protocol? (Choose two.)

used primarily as an EGP
uses Dijkstra’s algorithm to build the SPF tree
has an administrative distance of 100
automatically summarizes networks at the classful boundaries
calculates its metric using bandwidth

Explanation: Characteristics of OSPF include the following:
– Interior gateway protocol
– Link-state
– Classless
– Cost metric based on bandwidth
– Dijkstra algorithm
– Builds topological map
– Event-driven updates
– Hierarchical design
– Requires additional memory, CPU processing, and more initial bandwidth than other protocols

6. A router with two LAN interfaces, two WAN interfaces, and one configured loopback interface is operating with OSPF as its routing protocol. What does the router OSPF process use to assign the router ID?

the loopback interface IP address
the highest IP address on the LAN interfaces
the OSPF area ID that is configured on the interface with the highest IP address
the IP address of the interface that is configured with priority 0
the highest IP address that is configured on the WAN interfaces

Explanation: OSPF requires a unique router ID on each router. The router ID can be configured manually with the # router-id command. If this command is not issued, then the OSPF process will use the highest IPv4 address on an active interface as the router ID, with preference give to loopback interfaces.

7. Which verification command would identify the specific interfaces on a router that were configured with the passive-interface command?

show ip protocols
show ip eigrp neighbors
show ip interface brief
show ip route eigrp

Explanation: The show ip protocols command will identify interfaces that are configured as passive.

8. Which command, if applied on an OSPF router, would give a Gigabit Ethernet interface a lower cost than a Fast Ethernet interface?

(config-if)# bandwidth 100
(config-if)# ip ospf priority 1
(config-router)# auto-cost reference-bandwidth 1000
(config-if)# ip ospf cost 100

Explanation: OSPF uses the formula; Cost = 100,000,000 / bandwidth. Because OSPF will only use integers as cost, any bandwidth of 100 Mb/s or greater will all equal a cost of 1. To change this behavior, a new reference bandwidth can be configured. The new reference bandwidth will need to be larger than 100,000,000. In this case it needs to be 1,000,000,000. This is accomplished with the command auto-cost reference-bandwidth 1000, which means multiply the unit Mb/s by 1000. The result is 1,000,000,000.

9. A network administrator has just changed the router ID on a router that is working in an OSPFv2 environment. What should the administrator do to reset the adjacencies and use the new router ID?

Configure the network statements.
Change the OSPFv2 process ID.
Issue the clear ip ospf process privileged mode command.
Change the interface priority.

Explanation: If the router ID has changed on a working router, the OSPFv2 process must be cleared for the new router ID to take effect.

10. Which command can be used to view the OSPF hello and dead time intervals?

show ip ospf route
show ip protocols
show ip ospf interface
show ip ospf neighbor

Explanation: The OSPF hello and dead timers can be configured per interface. Hence, the correct command used to view the timers is the show ip ospf interface command. Adding the interface name and number to the command displays output for a specific interface.

11. What does the SPF algorithm consider to be the best path to a network?

The path that includes the fastest cumulative bandwidth links.
The path with the least number of hops.
The path with the smallest delays.
The path that includes the fastest single bandwidth link.

Explanation: Link-state protocols use accumulated cost to reach destination networks. The shortest path is not always the path with the least number of hops but instead the overall fastest pathway.

12. What is one use of the router ID in OSPF routing?

The router ID indicates the highest IPv4 address of all routers that are participating in OSPF routing.
The router ID identifies the OSPF area.
The router ID can be used to break a tie in the election process.
The router ID indicates the router priority value.

Explanation: The OSPF router ID uniquely identifies each router within an OSPF area, and allows each router to participate in the election process in that area. On multiaccess networks, if there is no router priority value configured on the routers, and if there is a tie in the election, the router with the highest router ID is elected DR. The router priority value is a value chosen by the administrator and manually configured on the router. The administrator can manually configure the router ID, or the router can automatically assign itself its highest IPv4 loopback or physical address as the router ID. That interface has to be up but does not have to be participating in the OSPF process.

13. What is the first criterion used by OPSF routers to elect a DR?

highest priority
highest router ID
highest MAC address
highest IP address

Explanation: When electing a DR, the router with the highest OSPF priority becomes the DR. If all routers have the same priority, then the router with the highest router ID is elected.

14. Which command could be used on a router to ensure that an OSPF adjacency is formed with another router?

show ip protocols
show ip ospf interface
show ip route
show ip ospf neighbor
show ip interface brief

Explanation: The show ip ospf neighbor command is a common command to use when an expected route does not appear in the routing table from the OSPFv2 routing protocol.

15. A router in an OSPF enterprise network has a default static route that has been configured via the interface that connects to the ISP. Which command would the network administrator apply on this router so that other routers in the OSPF network will use this default route?

redistribute connected
redistribute static
redistribute static subnets
default-information originate

Explanation: When an OSPF router is configured with a static route first and the default-information originate router configuration command is applied, the router declares itself to be the source of the default route information and propagates the default static route in OSPF updates to all other routers in the OSPF area.

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