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?
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
Quote from: dlots on February 08, 2017, 07:38:34 PM
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.
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
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.
Quote from: ggnfs000 on April 17, 2017, 12:21:46 AM
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.
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.
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.
I willprivate message you my answers as i dont want to look like a dummy.
Second thoughts can you send me the answers :(
:yeahright:
The answers are all in wikipedia and Cisco whitepapers. The study will do you well!
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?
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.
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
Quote from: deanwebb on May 17, 2017, 10:01:08 AM
:yeahright:
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.
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?
1) link speed thats is calculated in the LSDB gatehred from LSA's
4) Will need to look this up.
5) If you had a ip address duplicate on a loopback interface i am gathering that it would go to the next physical highest IP address. If you have two IP addresses the same on a physical interface you are going to have problems with routing.
6) Multi-access networks are the bounderies of the OSPF instance this includes all areas and can only have 1 Designated Router and 1 backup router at a time. If an organisations has more than one DR it would suggest that they have multipe multi-access networks.
7) Yes it was designed to see if i understood the process of router ID generation. ?
8) It allows you to manual setup your router IDS in a way they allows you to have control of the Router ID. ?
But i have a question am i right in saying that the router ID would not change until the OSPF instance is restarted ?
5 would be a good thing to lab up so that you could be sure.
Spot on with 8. The loopbacks allow for organizational structure to be created, independent of the IPs assigned by an ISP for an interface.
I think you are correct in your assumption. Best to test it in a quick lab, so you'll be sure.
Well brought this up in a lab.
Added the following
Interface loopback1
Ip address 1.1.1.1 255.0.0.0
ip ospf 1 area 0
this was added to both routers then restarted the router ID moved from physical ID to loopback ID. But they both now have the same router ID.
Now is this what i should have expected and would this not cause problems.
Output from Show ip ospf 1
Quote from: weasleman on May 17, 2017, 01:16:52 PM
Well brought this up in a lab.
Added the following
Interface loopback1
Ip address 1.1.1.1 255.0.0.0
ip ospf 1 area 0
this was added to both routers then restarted the router ID moved from physical ID to loopback ID. But they both now have the same router ID.
Now is this what i should have expected and would this not cause problems.
Output from Show ip ospf 1
I do believe that, yes, having two equally authoritative routers in an OSPF area is something that would cause problems. Cisco seems to agree on that account: http://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/23862-duplicate-router-id-ospf.html
Reading is one thing, you nod your head and move on. But labbing it... you begin to remember those lessons in your bones.
This is what you will look like after many hours of successful labbing:
:goku:
I totally agree my only frustration is that there is just so much to learn and know. Thanks for the time and i am enjoying this. its helping me get my head round things like you said reading and doing are totally different.
Here are my other answers.
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?
Destination unreachable ?
10. If you wanted all interfaces on a router to be in the same OSPF area, what command in config mode would you use?
interface range fa0/x-x ip ospf area x
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?
The maxium number of parrellel routes is four default is 1. Command maximum-path x
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?
the range value is from 1 to 65535
13. What is the largest number that can be assigned to an OSPF area?
4294967295
14. What is special about OSPF Area 0?
Its the backbone area
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?
they must have some type of bridge. Just looked it up inter area routing.
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?
No it will not yes 10.0.0.126 will
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?
Link state advertisements
LSA Type 1: Router LSA.
LSA Type 2: Network LSA.
LSA Type 3: Summary LSA.
LSA Type 4: Summary ASBR LSA.
LSA Type 5: Autonomous system external LSA.
LSA Type 6: Multicast OSPF LSA.
LSA Type 7: Not-so-stubby area LSA.
LSA Type 8: External attribute LSA for BGP.
Will we be expected to know all of these for the CCNA
18. How can routers be connected to the OSPF backbone area 0 through a non-backbone area?
Inter vlan routing. This is a guess and takes a cue from joining two autonomous systems in question 15
19. What abbreviation describes a router that joins an OSPF area to Area 0?
stub network
20. What is the benefit of having multiple OSPF areas in a large network? (three main benefits)
Breaks up the network into bits
Allows managebility
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?
Default setting 40
IP ospf hello-timer x
no ip ospf hello-interval x
clear ip ospf hello interval (guess)
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?
The DR will still be the same as it looks at the highest IP which is 10.254.254.254 the new router added will become the new BDR when OSPF is restarted. If the next router is added this will become the DR after ospf instance has been restarted as the IP is greater than the DR at present.
23. In OSPF, what happens to the routing table when a router stops getting hello packets from a neighbor?
The route will be removed and if more than one route this route will become the successor
24. In OSPF, what happens to the routing table when a router receives an LSA?
Nothing happens unless there is a change. If there is a change the database table will recalculate and populate the routing table.
25. What information can be used by a router running a link-state protocol to build and maintain its topological database? (Choose two.)
Link speed
and distance
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?
Hello packet
27. Which command is used to show all the OSPF link states?
Show ip OSPF x
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?
enable
config t
router ospf x
network 172.168.100.128 0.0.0.255 area 0
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
I would not have espected a subnet mask 0.0.0.255 area 0.0.0.255
9 - it's much worse than that... Much worse... Think about it: Router B gets a packet for a particular network and its default route points back to A...
16. Check your numbers again - are you sure on that one?
17. Know the ones that are used and then all the others are lumped in the "not used" category... you'll need to know them all for CCNP.
21. Don't guess on the second one. Best to look up the first line and see if there's an article that mentions a second, equivalent command as an alternative.
Good job on 22!
Also good job on 28! Very important to remember ALL the commands to use! Getting the proper order and usage on the simulations will be important.
9) Would this not cause a routing loop ? Ahhh now i have read the question
Router A is running OSPF Router B maybe or maybe not. Now the default AD for a default route is 1 which even if OSPF has on router B would take precedent over OSPF unless the route has been specified with a greater AD than OSPF. So the packet will ping from router A to Router B
16) no the 0.0.0.63 would not cover the address ranges. Apologies IPV4 still pickles my brain.
17) Will be looking at CCNP after CCNA. But it is useful to know.
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?
default setting is 40
ip ospf hello-interval 60
No ip ospf hello-interval x
The other command i cannot find. You could delete all config on the router this would change everything to default though :smug:
this stuff is starting to stick in my brain. THanks for the questions its helping I will wait for the EIGRP one next ;D hint hint.
I will throw in some questions because I had to deal with this today.
9 - Does the packet ever stop going back and forth between router A and B? Why or why not? What happens if instead of 1 packet I send 1,000 packets, or 10,000 packets?
-Otanx
Hi Otanx,
I would expect that in time the packet would expire.....Yes just looked this up it counts down its ttl. As for sending more packets i would expect that bandwidth on the lines to shrink to a point where its the equivalent of a broadcast storm in effect. unresponsive network.
Quote from: weasleman on May 18, 2017, 10:10:28 AM
this stuff is starting to stick in my brain. THanks for the questions its helping I will wait for the EIGRP one next ;D hint hint.
I've got 16 years of experience as a teacher, you better believe I can ask some good questions! :matrix: :professorcat:
I have a lot of information floating around in my brain. this Forum is now joining the dots. Well some of it.
Still stuck on
IP OSPF hello-interval
Ebveryone seems to use no ip OSPF hello-interval x
Quote from: weasleman on May 17, 2017, 04:07:26 PM
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?
Link state advertisements
LSA Type 1: Router LSA.
LSA Type 2: Network LSA.
LSA Type 3: Summary LSA.
LSA Type 4: Summary ASBR LSA.
LSA Type 5: Autonomous system external LSA.
LSA Type 6: Multicast OSPF LSA.
LSA Type 7: Not-so-stubby area LSA.
LSA Type 8: External attribute LSA for BGP.
Will we be expected to know all of these for the CCNA
for IPv4 there are only 7 LSA type, I don't recall the External attribute LSA for BGP]
for IPv6 there are 2 additional LSA types
LSA Type 8 – Link LSA
Link-LSAs have link-local flooding scope. A router originates a separate link-LSA for each attached link that supports two or more (including the originating router itself) routers. Link-LSAs have three purposes:
1. They provide the router's link-local address to all other routers attached to the link.
2. They inform other routers attached to the link of a list of IPv6 prefixes to associate with the link.
3. They allow the router to advertise a collection of Options bits in the network-LSA originated by the Designated Router on a broadcast or NBMA link.
LSA Type 9 – Intra-Area Prefix LSA
An intra-area-prefix-LSA has one of two functions:
1. It either associates a list of IPv6 address prefixes with a transit network link by referencing a network-LSA...
2. Or associates a list of IPv6 address prefixes with a router by referencing a router-LSA.
I am just getting to IPV6. IPV4 still causing me a headache at times but i will get there.