OSPF for Interconnecting Cisco Networking Devices Part 1 (100-105) CCENT CCNA

[deanwebb]

OSPF Review for ICND 100-105

1. OSPF is a link-state routing protocol. How does it update routing tables? Does it share routing tables with neighbors? How does it calculate the ideal route to a destination?

2. How does OSPF confine routing instability?

3. How is OSPF cost calculated?

4. In OSPF, what is a process ID? What is the process ID used for? Does it need to be the same on all routers in an area? What is the range of values that can be used for a process ID?

5. In OSPF, what happens if more than one router is configured with the same router ID?

6. In OSPF, what is a multi-access network?
How many DRs are required per multi-access network? What is the maximum number of routers per multi-access network?
If there was more than one OSPF DR in a network, what would you be able to determine about the number of multi-access networks on the network?

7. On a router that has interfaces configured with IP addresses of 10.1.1.1, 172.16.1.1, 192.168.1.1, and 126.86.12.99, which one will be used by default as the router ID by the OSPF process?
If, on the same router, a loopback interface is given an IP address of 10.0.0.1, will that change the OSPF router ID? If so, what will the router ID become?

8. In OSPF, what are two advantages to configuring a loopback address over using only interface addresses?
(Hint: One is for availability, the other is for organization)

9. RouterA has OSPF configured correctly and a default route that directs traffic to RouterB. RouterB has a default route that directs traffic to RouterA. What happens if RouterA sends a packet to RouterB that RouterB does not have a specific route defined for?

10. If you wanted all interfaces on a router to be in the same OSPF area, what command in config mode would you use?

11. In OSPF, what is the maximum number of parallel routes it can support? What is the default number of parallel routes? What command can be used to change the default setting?

12. An admin wants his OSPF process ID to be 66666 because he likes sixes. What specific limitation of OSPF will just break his heart?

13. What is the largest number that can be assigned to an OSPF area?

14. What is special about OSPF Area 0?

15. If OSPF Area 57883 is to share information with OSPF Area 9871, what must be true in the OSPF topology for that to succeed?

16. If you enter the command "network 10.0.0.128 0.0.0.63 area 0", will an interface with an IP of 10.0.0.130 participate in OSPF? What about an interface with an IP of 10.0.0.126?

17. What are OSPF LSAs? What are the different types of LSAs? If a network is set up to have just one OSPF area, what kind of LSAs will not be used?

18. How can routers be connected to the OSPF backbone area 0 through a non-backbone area?

19. What abbreviation describes a router that joins an OSPF area to Area 0?

20. What is the benefit of having multiple OSPF areas in a large network? (three main benefits)

21. What is the default setting for the hello timer for OSPF on a Cisco router? What command can be used to change that value to 60 seconds? What two different commands will return the router to its default state, once you realize that having one set for 60 seconds means it won't work well with the other routers still on default settings?

22. In a network, the core router has a loopback address of 10.254.254.254, and all other routers have loopback addresses configured in the 10.0.0.0 /24 range. What happens as far as DRs are concerned if someone in a branch office attaches a router with a loopback of 10.200.200.200? What happens if, after that, someone attaches a router with a loopback of 10.255.255.254?

23. In OSPF, what happens to the routing table when a router stops getting hello packets from a neighbor?

24. In OSPF, what happens to the routing table when a router receives an LSA?

25. What information can be used by a router running a link-state protocol to build and maintain its topological database? (Choose two.)

26. An admin is examining a trace of network traffic and sees packets bound for 224.0.0.5. What OSPF packet corresponds with that destination?

27. Which command is used to show all the OSPF link states?

28. An admin wants to add 172.16.100.128 /25 to OSPF area 0.
Assuming he is starting at a > prompt, what are the commands that need to be entered to accomplish this task?

29. Below is what someone typed in for an OSPF configuration. Without looking at any other part of the device config, what potential problem can you spot in these lines of code?

Router(config)# router ospf 1

Router(config-router)# network 192.168.1.0 255.255.255.0 area 0

30. LAB TIME!

In Packet Tracer or GNS3 or in your home lab, set up 2 routers and set up a link between them. Configure OSPF on each of them. On the first router, define a route for 172.16.0.0/16, 172.17.0.0/16, 172.18.0.0/16, and 172.19.0.0/16 each out of an interface not connecting it to the second router. On the second router, define routes for 192.168.1.0/26, 192.168.1.64/26, 192.168.1.128/26, and 192.168.1.192/26 each out of an interface not connecting it to the first router.

What are the differences between the routing tables of the first and second routers?

What happens to the routing tables if all the routes on each router point to the same interface? What happens to the routing tables if the routes are not all via the same interface?

Now change the hello and dead timers on the first router. What happens to the routers' adjacency?

[dlots]

Did you want answers? or just to put a list of questions together?

Didn't want to make spoilers if you didn't want them

[deanwebb]

Did you want answers? or just to put a list of questions together?

Didn't want to make spoilers if you didn't want them

Feel free to add answers and explanations with [ spoiler ] tags.

[icecream-guy]

did you see Pepelnjak's  blog today? The Unintended Consequences of NSSA Kludges.. interesting

http://blog.ipspace.net/2017/02/the-unintended-consequences-of-nssa.html

[ggnfs000]

Are there any other 200-105 topics aside from ospf expected on 100- 105 exam? I literally read two chapters of 200-105 to compete reading for 100-105 exam.

[deanwebb]

Are there any other 200-105 topics aside from ospf expected on 100- 105 exam? I literally read two chapters of 200-105 to compete reading for 100-105 exam.

I'm about to post the rest of my study questions for 100-105. I just went with the topics from the syllabus and ran with my imagination.

[ggnfs000]

I spent about 2-3 days studying ospf, did not expect to be become fully proficient but at least can do a basic setup without reading book. Its chapters are followed by EIGRP and being most commonly used protocol, do you expect to see in 100-105? At least in the book for 100-105 I have, there is absolute no mentioning of OSPF or EIGRP.

[deanwebb]

OSPF is definitely on 100-105. My son took a LOT of hits on this one, so that's why I went after that area first.

This covers all the basics, and that's what the test covers. ALL the basics.

[weasleman]

I willprivate message you my answers as i dont want to look like a dummy.

Second thoughts can you send me the answers

[deanwebb]

The answers are all in wikipedia and Cisco whitepapers. The study will do you well!

[weasleman]

I was trying to be lazy but i get you.

I am going through the study stuff now and i find that everytime i think i have something nailed i learn something else and puts me right back at the beginning of my studying.

So i have a question is it really posible to learn Routing a switching in 6 days doing a boot camp?

Because every time i learn something it leads to another question.

or are the bootcamps designed just to pass the exam?

[deanwebb]

Pretty much, yeah... no long-term memory or real skill comes out of a boot camp. We're actually far enough down in the thread to where we could post answers here and the questions above would still be usable as review questions. You want to do the honors and start posting what you got? Then we can discuss some of the finer points of the basics.

It will be well worth your time in so doing, I promise.

[weasleman]

1. OSPF is a link-state routing protocol. How does it update routing tables? Does it share routing tables with neighbors? How does it calculate the ideal route to a destination?

It creates Link state advertisements LSA's. Yes it shares routing table information via LSA's after it creates adjecencies. All these are combined into LSDB where links are calculated and successor is placed into the routing table.

2. How does OSPF confine routing instability?

By allowing you to break up the network into areas which would allow you to manage instabilities.

3. How is OSPF cost calculated?

By combining link speeds to find the path with the lowest cost.

4. In OSPF, what is a process ID? What is the process ID used for? Does it need to be the same on all routers in an area? What is the range of values that can be used for a process ID?

No the Process ID is local and is used by the router to manage processes. Each router will have its own process id.

5. In OSPF, what happens if more than one router is configured with the same router ID?

it will look at the Loopback IP address first and find the highest IP which will become its id if no loop back the highest Physical IP will be used. Which would suggest you have duplicate IP's somewhere.

6. In OSPF, what is a multi-access network?
How many DRs are required per multi-access network? What is the maximum number of routers per multi-access network?
If there was more than one OSPF DR in a network, what would you be able to determine about the number of multi-access networks on the network?

This is the areas that encompass the OSPF domain and contains all areas. there will be one DR and one BDR. I am not sure how many but i would say this depends on areas i am gathering?
You have two instances of OSPF running at the same time within the network.


7. On a router that has interfaces configured with IP addresses of 10.1.1.1, 172.16.1.1, 192.168.1.1, and 126.86.12.99, which one will be used by default as the router ID by the OSPF process?
If, on the same router, a loopback interface is given an IP address of 10.0.0.1, will that change the OSPF router ID? If so, what will the router ID become?

192.168.1.1
it will change but that would be after the OSPF instance has been restarted.
Router id 10.0.0.1

8. In OSPF, what are two advantages to configuring a loopback address over using only interface addresses?
(Hint: One is for availability, the other is for organization)

The loopback will never go down
Allows you to create Router ID's

heres a few still working on the others. It was late when i started these last night

[NetworkGroover]

The answers are all in wikipedia and Cisco whitepapers. The study will do you well!

Not to mention learning how to research if you plan on seriously pursuing this career.  That will be vital.  Especially if you run into bleeding edge tech that hasn't been around for 20 years such that there's a library of documentation on it easily at hand.

[deanwebb]

Gonna follow up now...

1. So how is the best route selected in OSPF?

4. What is the range of numbers for process ID?

5. Keep going with the duplicate IP addressess... what happens in that case?

6. You've got a few details to get into here... one thing this exercise will teach is the need to be complete in one's answers. This is true on the certification exam, even more so when in engineering discussions.

7. I hope you see why 8. was the follow up question to this one.

8. Not just router IDs - what does the loopback allow in this regard? Think about if you were working on a network with 200+ routers, how would you want that set up in terms of OSPF router IDs?