New CCNA OSPF Questions and Answers with Explanation

By | September 28, 2017

This is an Updated CCNA OSPF exam question (2016). You might see a different IP addressing, Port allocation and Configurations.

As usual, take time and read through the question so as to clearly understand what you are required to do.

Note: These OSPF Questions are used for demonstration only, you will see a slightly different use of grammar and context, IP addressing, Port allocation in the real CCNA exam. But it all works the same way if you could just grasp the technique.

Question 1

Refer to the exhibit.

The network above is configured with OSPF protocol. Router A could not form an adjacency with router B, what is the possible cause?

A. The loopback addresses are on different subnets.

B. The values of the dead timers on the routers are different.

C. Route summarization is enabled on both routers.

D. The process identifier on router A is different than the process identifier on router B.

Answer: B

Explanation:

The term adjacencies simply mean the conditions to become OSPF neighbor. Once the adjacency has been established between a pair of routers, we say that now they are OSPF neighbors.

Adjacent OSPF neighbors exchange LSDB information in the form of LSAs in addition to HELLO packets. Their normal stable neighbor state is FULL. For example, when two routers are connected via serial link, or the relation between DR and BDR, or DR and DROther

To form an adjacency (become neighbor), router A & B must have the same Hello interval, Dead interval, and AREA numbers

Question 2

Refer to the exhibit:

Why do large OSPF networks use a hierarchical design? (Choose three.)

A. to decrease latency by increasing bandwidth

B. to reduce routing overhead

C. to speed up convergence

D. to confine network instability to single areas of the network

E. to reduce the complexity of router configuration

F. to lower costs by replacing routers with distribution layer switches

Answer : B,C,D

Explanation

For a large OSPF networks, it’s a good recommendation to use a hierarchical design. Multiple areas connect to a distribution area, or which is also called the backbone (area 0).

The design approach allows for extensive control of routing updates. Area definition reduces routing overhead, speeds up convergence, confines network instability to an area, and improves performance.

Any changes in one area are contained to that area only, not to the neighboring router within the entire network. Confining the topology changes to one area reduces the overhead and speeds the convergence of the network

Question 3

A network administrator is troubleshooting an EIGRP problem on a router and needs to confirm the IP addresses of the devices with which the router has established adjacency. The retransmit interval and the queue counts for the adjacent routers also need to be checked. What command will display the required information?

A. Router# show ip eigrp adjacency

B. Router# show ip eigrp topology

C. Router# show ip eigrp interfaces

D. Router# show ip eigrp neighbors

Answer : D

Explanation:

Using the show ip eigrp neighbors command will display the output below:

 The retransmit interval (Smooth Round Trip Timer SRTT) and the queue counts (Q count, which shows the number of queued EIGRP packets) for the adjacent routers are listed:




Question 4

Which two are advantages of static routing when compared to dynamic routing? (Choose two.)

A. Configuration complexity decreases as network size increases.

B. Security increases because only the network administrator may change the routing table.

C. Route summarization is computed automatically by the router.

D. Routing tables adapt automatically to topology changes.

E. An efficient algorithm is used to build routing tables, using automatic updates.

F. Routing updates are automatically sent to neighbors.

G. Routing traffic load is reduced when used in stub network links.

Answer: B, G

Explanation:

Since static routing is when you manually enter the routing configuration on the router interface(s). This is believed to be more secure (and more prone to human errors) since the network administrator will need to make changes to the routing table directly.

Also, in stub networks where there is only a single uplink connection, the load is reduced as stub routers just need a single static default route, instead of many routes that all have the same next hop IP address.

Question 5

What are two enhancements that OSPFv3 supports over OSPFv2? (Choose two.)

A. It requires the use of ARP.
B. It can support multiple IPv6 subnets on a single link.
C. It supports up to 2 instances of OSPFv3 over a common link.
D. It routes over links rather than over networks.
Answer: B, D

Explanation:

Question 6

Which characteristics are representatives of a link-state routing protocol? (Choose three.)

A. provides common view of entire topology

B. exchanges routing tables with neighbors

C. calculates the shortest path

D. utilizes event-triggered updates

E. utilizes frequent periodic updates

Answer : A,C,D

Explanation:

 Each of routers running link-state routing protocol learns paths to all the destinations in its area.

 Link-state routing protocols generate routing updates only (not the whole routing table) when a change occurs in the network topology so Link-state routing protocol like OSPF uses Dijkstra algorithm to calculate the shortest path. Unlike Distance vector routing protocol (which utilizes frequent periodic updates), link-state routing protocol utilizes event-triggered updates (only sends update when a change occurs)



Question 7

Refer to the exhibit.

Given the output of this command, if the router ID has not been manually set, what router ID will OSPF use for this router?

A. 10.1.1.2

B. 10.154.154.1

C. 172.16.5.1

D. 192.168.5.3

Answer: C

Explanation:

The highest IP address of all loopback interfaces will be chosen. Loopback 0 will be chosen as the router ID.

Question 8

What information does a router running a link-state protocol use to build and maintain its topological database? (Choose two.)

A. hello packets

B. SAP messages sent by other routers

C. LSAs from other routers

D. beacons received on point-to-point links

E. routing tables received from other link-state routers

F. TTL packets from designated routers

Answer: A, C

Explanation:

Neighbor discovery is the first step in getting a link state environment up and running by using a Hello packet protocol.

After the discovery and info exchange, the adjacencies are established, the routers may begin sending out LSAs (advertisements) to every neighbor. In turn, each received LSA is copied and forwarded to every neighbor except the one that sent the LSA.

Question 9

What OSPF command, when configured, will include all interfaces into area 0?

A. network 0.0.0.0 255.255.255.255 area 0

B. network 0.0.0.0 0.0.0.0 area 0

C. network 255.255.255.255 0.0.0.0 area 0

D. network all-interfaces area 0

Answer : A

Explanation:

The network configuration command:  network 0.0.0.0 255.255.255.255 area 0 dictates that all IP address that is enabled on any interface,  should be placed in area 0. router ospf 1 network 0.0.0.0 255.255.255.255 area 0

Reference: http://www.ciscopress.com/articles/article.asp?p=26919&seqNum=3

Question 10

Refer to the exhibit.

looking at the given output, the router has not had its router ID set manually, what value will OSPF use as its router ID?

A. 192.168.1.1

B. 172.16.1.1

C. 1.1.1.1

D. 2.2.2.2

Answer : D

Explanation:

 If a router-id is not configured manually in the OSPF routing process the router will automatically configure a router-id determined from the highest IP address of a logical interface (loopback interface) or the highest IP address of an active interface. If more than one loopback interfaces are configured, the router will compare the IP addresses of each of the interfaces and choose the highest IP address from the loopbacks.