CCNA And CCENT Cisco Certification Exam Questions:

10 Questions On OSPF

By Chris Bryant, CCIE #12933

You can't earn your CCNA without mastering OSPF, and here are 10 practice questions to help you do just that!

In the answer section, you'll also find a tutorial on OSPF hello and dead timers. (Answers can be found at the bottom of the page.)

Enjoy! Also, be sure to take my other CCNA and CCENT practice exams!

Five Minutes From Now, You Can Be Studying For CCNA Exam Success Just As Thousands Of Other CCNA Candidates Around The World Have - With Chris Bryant, CCIE #12933 With You Every Step Of The Way - With The Ultimate CCNA Exam Study Package!

1. Which of the following terms describe OSPF?

A. refers to its metric as "distance"

B. refers to its metric as "cost"

C. is a link-state protocol

D. is a hybrid of link-state and distance-vector routing

E. uses the concept of successor and feasible successors

2. Which of the following algorithms does OSPF use?

A. SPF

B. Dijkstra

C. DUAL

D. Bellman-Ford

 

3. Short answer: What command resulted in the following output?

OSPF Router with ID (1.1.1.1) (Process ID 1)

                Router Link States (Area 0)

Link ID         ADV Router      Age         Seq#       Checksum Link
1.1.1.1         1.1.1.1         54          0x80000002 0xDCA2   1
2.2.2.2         2.2.2.2         33          0x80000005 0x98DA   1
172.23.23.3     172.23.23.3     7           0x80000003 0xCEF9   1

4. Match the protocols RIPv1, RIPv2, OSPF, and EIGRP to their respective reserved address. Not all addresses will be chosen.

A. 224.0.0.10

B. 224.0.0.7

C. 255.255.255.10

D. 255.255.255.255

E. 224.0.0.9

F. 224.0.0.5

G. 224.0.0.4

 

5. In a hub-and-spoke OSPF NBMA network, which router should serve as the Designated Router?

 

6. What is the recommended method of carrying the task out described in Question 5?

 

7. Identify the true statements regarding OSPF hello and dead times on Ethernet segments.

A. The default hello time is 10 seconds.

B. The default hello time is 30 seconds.

C. The default hello time is 60 seconds.

D. The dead time is four times the hello time.

E. The dead time is not determined in any way by the hello time.

F. Changing the hello time dynamically changes the dead time as well.

G. To change the dead time, you must do so statically with the ip ospf dead-time command.

8. What command resulted in the following output?

R2# ?
00:54:19: OSPF: Rcv hello from 172.12.23.3 area 0 from Ethernet0 172.12.23.3
00:54:19: OSPF: Mismatched hello parameters from 172.12.23.3
00:54:19: Dead R 40 C 60, Hello R 10 C 15  Mask R 255.255.255.128 C 255.255.255.128

9. What command resulted in the following output? Describe the value shown under each category.

R2# ?

Neighbor ID     Pri   State       Dead Time   Address        Interface
172.12.23.3       1   FULL/DR     00:00:36    172.12.23.3    Ethernet0

10. Put the following OSPF neighbor adjacency states in order, starting with the earliest state.

A. Exstart

B. Loading

C. 2-way

D. Init

E. Full

F. Exchange

G. Down

H. Attempt

 

Answers right after this message!

To earn the new CCNA Security, Wireless, and Voice certifications, you've got to earn your CCNA first... and here's how to do just that!

Five Minutes From Now, You Can Be Studying For CCNA Exam Success Just As Thousands Of Other Candidates Around The World Have - With Chris Bryant, CCIE #12933 With You Every Step Of The Way - With The Ultimate CCNA Exam Study Package!

Here are the answers to today's questions!

1. B, C. OSPF is a link-state protocol, and the OSPF metric you'll see in a routing table is referred to as cost.

2. A, B. OSPF's algorithm is known as the Dijkstra algorithm and the SPF algorithm - Shortest Path First.

3. That's the output of the show ip ospf database command.

4. RIPv1's update packet destination address is the broadcast address 255.255.255.255. Here are the addresses used by the other protocols mentioned in this question:

RIPv2 - 224.0.0.9

EIGRP - 224.0.0.10

OSPF - 224.0.0.5

5. The hub router should be configured as the Designated Router (DR).

6. The preferred method is to set the OSPF interface priority to zero on the appropriate interfaces on the spoke routers while leaving the hub's OSPF interface priority at the default of one.

7. A, D, F. On broadcast segments, the OSPF hello time is 10 seconds. As with other segment types, the OSPF dead time is four times the hello time. If you change the hello time, the dead time dynamically adjusts.

Let's take a look at each of those statements in action. R2 and R3 have formed an OSPF adjacency over their respective Ethernet0 interfaces. Here is the partial result of show ip ospf interface e0 on R2. Note the hello and dead timers.

R2#show ip ospf int e0
Ethernet0 is up, line protocol is up
Internet Address 172.12.13.2/24, Area 0
Process ID 1, Router ID 172.12.123.2, Network Type BROADCAST, Cost: 10
Transmit Delay is 1 sec, State BDR, Priority 1
Designated Router (ID) 172.12.123.3, Interface address 172.12.13.3
Backup Designated router (ID) 172.12.123.2, Interface address 172.12.13.2
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5

I'll use the ip ospf hello command on R2's ethernet0 interface to double the hello time.

R2(config-if)#ip ospf hello 20
R2(config-if)#^Z

R2#show ip ospf int e0
Ethernet0 is up, line protocol is up
Internet Address 172.12.13.2/24, Area 0
Process ID 1, Router ID 172.12.123.2, Network Type BROADCAST, Cost: 10
Transmit Delay is 1 sec, State BDR, Priority 1
Designated Router (ID) 172.12.123.3, Interface address 172.12.13.3
Backup Designated router (ID) 172.12.123.2, Interface address 172.12.13.2
Timer intervals configured, Hello 20, Dead 80, Wait 80, Retransmit 5
Hello due in 00:00:09

Note that both the hello and dead timers changed!

And of course, you know what happened just 9 seconds later...

R2#
2d00h: %OSPF-5-ADJCHG: Process 1, Nbr 172.12.123.3 on Ethernet0 from FULL to DOWN, Neighbor Down: Dead timer expired

That's what happens when the OSPF hello and dead timers do not match - even after the adjacency has formed!

8. That's the output of debug ip ospf adj, and that output illustrates what we saw happen in the last question - mismatched OSPF hello parameters result in a downed adjacency.

9. That's the output of show ip ospf neighbor. From left to right, you'll see...

Neighbor ID: The OSPF RID of the neighbor.

Pri: Short for "priority", that's the interface priority of the neighbor.

State: That's the OSPF adjacency state and role of the router - DR, BDR, or DROTHER.

Dead Time: Time remaining until the adjacency is torn down. Receipt of a valid hello packet will reset this timer.

Address: The IP address of the neighbor's interface through which the adjacency is formed.

Interface: The interface through which the adjacency has formed.

10. The order is Down, Attempt, Init, 2-Way, Exstart, Exchange, Loading, and Full.

Whew! While you're here, take a look at the CCNA Study Package - it's helped thousands of CCNA candidates around the world earn their certification, and it will do the same for you!

Five Minutes From Now, You Can Be Studying For CCNA Exam Success Just As Thousands Of Other CCNA Candidates Around The World Have - With Chris Bryant, CCIE #12933 With You Every Step Of The Way - With The Ultimate CCNA Exam Study Package!

To your success,

Chris Bryant

CCIE #12933

chris@thebryantadvantage.com