CCNA – OSPF Questions
Here you will find answers to OSPF Questions
Note: If you are not sure about OSPF, please read my OSPF tutorial
Question 1
Which of the following statements below best describe the process identifier that is used to run OSPF on a router? (Choose two)
A – It is an optional parameter required only if multiple OSPF processes are running on the router
B – It is locally significant
C – It is needed to identify a unique instance of an OSPF database
D – All routers in the same OSPF area must have the same process ID if they are to exchange routing information
Answer: B C
Question 2:
Why R1 can’t establish an OSPF neighbor relationship with R3 according to the following graphic? (Choose two)
A – Configure EIGRP on these routers with a lower administrative distance
B – All routers should be configured for backbone Area 1
C – R1 and R3 have been configured in different areas
D – The hello and dead interval timers are not configured the same values on R1 and R3
Answer: C D
Explanation:
A is not correct because configure EIGRP on these routers (with a lower administrative distance) will force these routers to run EIGRP, not OSPF.
B is not correct because the backbone area of OSPF is always Area 0.
C and D are correct because these entries must match on neighboring routers:
- Hello and dead intervals
– Area ID (Area 0 in this case)
– Authentication password
– Stub area flag
Question 3:
Which items are correct about the routing protocol OSPF? (Choose three)
A – Support VLSM
B – Increase routing overhead on the network
C – Confine network instability to one area of the network
D – Allow extensive control of routing updates
Answer: A C D
Explanation:
Routing overhead is the amount of information needed to describe the changes in a dynamic network topology. All routers in an OSPF area have identical copies of the topology database and the topology database of one area is hidden from the rest of the areas to reduce routing overhead because fewer routing updates are sent and smaller routing trees are computed and maintained (allow extensive control of routing updates and confine network instability to one area of the network).
Question 4:
Which three features are of OSPF routing protocol? (Choose three)
A – Converge quickly
B – OSPF is a classful routing protocol
C – Identify the best route by use of cost
D – Before exchanging routing information, OSPF routers find out neighbors
Answer: A C D
Question 5:
OSPF routing uses the concept of areas. What are the characteristics of OSPF areas? (Chose three)
A – Each OSPF area requires a loopback interface to be configured
B – Areas may be assigned any number from 0 to 65535
C – Area 0 is called the backbone area
D – Hierarchical OSPF networks do not require multiple areas
E – Multiple OSPF areas must connect to area 0
F – Single area OSPF networks must be configured in area 1
Answer: B C E
Explanation:
I used to think the answers should be C D E and here is my explanation:
OSPF can use an active interface for its router ID, so a loopback interface is not a must -> A is incorrect.
OSPF Area is a 32-bit number so we can use up to 232 – 1 = 4294967296 – 1 (since Area 0 is the first area). Remember that only process ID is a 16-bit number and ranges from 1 to 65535 -> B is incorrect.
F is incorrect too because single area OSPF netwoks must be configured in Area 0, which is called the backbone area.
For answer D, it is a bit hard to guess what they want to say about “hierarchical” but we should understand “Hierarchical OSPF networks” as “OSPF networks”. D is correct bercause we can only have one area (area 0 – the backbone area) for our networks.
But TT commented on 01-11-2010:
Especially to note on choice B, D, and E:
Choice B: we all know that The areas can be any number from 0 to 4.2 billion and 1 to 65,535 for the Process ID. As choice B specifies ‘area’ (be aware, it’s not saying ‘process id), there is no reason to say that we cannot assign numbers from 0 to 65535 for area # (it is using ‘may be’, not ‘have to be’ or ‘ought to be’). Hence, we do not worry about assigning ’0′.
Choice E: as Area 0 is the backbone, we all understand that any areas in a OSPF network have to be connected to it. And actually this is implicitly saying that multiple areas form a hierarchical OSPF network, as Area 0 being a root and others being its leaves.
Choice D: when it specifies ‘Hierarchical’, at least 2 areas should be required to form such topology (of course that includes Area 0)
Although Choice B is not an absolutely accurate statement since it not only can be assigned up to 65535, it is still a correct answer. And again, it specifies ‘area’, not ‘process id’, so ’0′ can be included. Finally, it would be meaningless to call OSPF a hierarchical network if no more than one area is present.
—————————————————————————————————-
I reviewed the question and think it is a more suitable solution with choice B than choice D, surely it is a tricky question!
Question 6:
Part of the OSPF network is shown below:
Configuration exhibit:
R1 routing commands:
ip route 0.0.0.0 0.0.0.0 serial0/0
router ospf 1
network 172.16.100.0 0.0.0.3 area 0
network 172.16.100.64 0.0.0.63 area 0
network 172.16.100.128 0.0.0.31 area 0
default-information originate
You work as a network technician, study the exhibits carefully. Assume that all router interfaces are operational and correctly configured. In addition, assume that OSPF has been correctly configured on router R2. How will the default route configured on R1 affect the operation of R2?
A – Any packet destined for a network that is not directly connected to router R2 will be dropped immediately
B – Any packet destined for a network that is not directly connected to router R1 will be dropped
C – Any packet destined for a network that is not directly connected to router R2 will be dropped immediately because of the lack of a gateway on R1
D – The network directly connected to a router R2 will not be able to communicate with the 172.16.100.0, 172.16.100.28 and 172.16.100.64 subnetworks.
E – Any packet destined for a network that is not referenced in the routing table of router R2 will be directed to R1. R1 will then send that packet back to R2 and a routing loop will occur
Answer: E
Explanation:
First, notice that the more-specific routes will always be favored over less-specific routes regardless of the administrative distance set for a protocol. In this case, because we use OSPF for three networks (172.16.100.0 0.0.0.3, 172.16.100.64 0.0.0.63, 172.16.100.128 0.0.0.31) so the packets destined for these networks will not be affected by the default route.
The default route configured on R1 “ip route 0.0.0.0 0.0.0.0 serial0/0″ will send any packet whose destination network is not referenced in the routing table of router R1 to R2, it doesn’t drop anything so answers A, B and C are not correct. D is not correct too because these routes are declared in R1 and the question says that “OSPF has been correctly configured on router R2″, so network directly connected to router R2 can communicate with those three subnetworks.
As said above, the default route configured on R1 will send any packet destined for a network that is not referenced in its routing table to R2; R2 in turn sends it to R1 because it is the only way and a routing loop will occur.
Q6:
the answer says that packets on reaching r2,if no entries are found in the routing table then by default it will be routed to r1.
my question is how is it even possible as default route is not added in r2 ??
the packets ll be discarded acc to my knowledge and i even feel that there is no suitable answer for this question.
please correct me if i am wrong
I have some confusion regarding Router ID. I know Highest Physical IP has been Router ID for router. but Highest in which?? in digit or in terms of first to Last IP.
suppose there are 2 IPs 10.20.30.45 and 10.20.30.48. so which one become router id 1st one or 2nd one.?? kindly replay..as i am going for exmaniation in next week
@Arpit
In your example 10.20.30.48 becomes the router ID.
In other instances such as: 10.20.30.48…..172.16.12.37…192.168.23.27…..router ID will be 192.168.23.27. This is what is meant by highest physical IP. And must be in the “up” state.
I hope this help.
@anup:
Look OSPF configuration on R1:
router ospf 1
default-information originate
…
command: “default-information originate” says OSPF to redistribute default route into OSPF routing domain.
And default route must be defined on this router. This router automatically becomes ASBR.
R2#show ip rou
…
Gateway of last resort is 172.16.100.1 to network 0.0.0.0
172.16.0.0/16 is variably subnetted, 6 subnets, 5 masks
C 172.16.0.0/20 is directly connected, FastEthernet0/1
C 172.16.16.0/20 is directly connected, FastEthernet0/0
C 172.16.32.0/22 is directly connected, FastEthernet1/0
C 172.16.100.0/30 is directly connected, Serial0/3/0
O 172.16.100.64/26 [110/782] via 172.16.100.1, 00:00:03, Serial0/3/0
O 172.16.100.128/27 [110/782] via 172.16.100.1, 00:00:03, Serial0/3/0
O*E2 0.0.0.0/0 [110/1] via 172.16.100.1, 00:00:03, Serial0/3/0
Try to design this network in Packet tracer.
@anup:
Gateway of last resort is 172.16.100.1 to network 0.0.0.0
I.e. link to R1 becomes default gateway for R2.
i had no idea of default-info originate….thanks a lot dimS…..
someone please send me the lastest dump abm.mzkhan@gmail.com
This site is really helpful, i am taking my CCNA exam coming week. Can anybody send me some latest dumps or some hints that can help me to pass the exams. insushaay@gmail.com
Thanks
insushaay
Hello 9tut,
Q5: Answer B is incorrect as mentioned in detail from your side. but in Answer you mentioned B C & E. Kindly update
Regard’s
all OSPF routers have default priority as 1(possible priorities are 0 to 255)
priority 0 means forcefull DR others
priority 255 means forcefull DR
If all routers have same priority the election go on router ID,
iN ANY CASE IF DR FAILS THEN BDR become DR ,once BDR become DR ,it remains DR .(even if the original DR comes up ,it cannot claim for the same)
Can any one tell me if the loopback interfaces receiving the routing the updates?????
9tut
Question 5 seems to have a clash in regards to the answer and the explanation. The answer is B, C, E, but in the explanation it says “B is incorrect”.
I have read the comments, and also all of your comments, and one guy stated that this is english grammatical nonsense and has nothing to do with precision of the answers in terms of CCNA technicalities.
I’m so confused! Can anybody shed any light on this subject? The dump im using atm states C, D, E as the correct answer.
Cheers
Passed exam today! 841.
Thanks for your info.
@9tut: I think Answer of Q6 can be explained like this: R2 obtain the full routing table from R1 and find that R1 has default route..so anythinng undestined packet from R2 will forward to R1. and again R1 will send it to R2..then routing loops will occur..
ans of question no 5 should be “C D E” according to todd lammle. same question given in the book..
sir
i had to configured ospf configuration but it can’t be work properly. i have to add all network bu port does not up
thanx you
Sir
IF suppose we have two routers and running OSPF (say router 1 and router 2) now the loopback IP of both the routers are different but the physical interface ip of both the routers are same and it is P2P OSPF link. Then my question is – whether routers will be able to form neighbor relationship ???
Question #5 is B, C, E! Answer D makes no sense because hierarchical area is more than one area and it will need multiple area! If you only have area 0 then its not hierarchical.
I agree with Bruno. What are they testing for ? Knowledge of Cisco devices or English? And, the ridiculous part is: companies out there that will not give someone a chance because they don’t have these stupid certs.
q6: the explanation is not clear — how does R2 send the packet back to R1 — I usually find easy explanations on wikipedia site — but this time I did not — please explain how r2 sends packet back to r1
q6: I guess that the answer is in the understanding of how ospf really works–
Question five’s answers don’t match up with the explanation. Please correct.
@geedub
Q6.
There’s a loop in the topology. You should take one step back and analyze what is causing the loop, and that will eliminate some of the questions you are asking.
This topology does not have ” a route of last resort” set yet, OR actually “route of last resort” is not properly configured. Therefore causing a routing loop.
Question 6:
the right choice is E, but the reason is that there is a “default-information originate” command in R1.
The above command tells every one to come to R1. If we had ommited it then no routing loop would be accured.
Q.6:- The default route configured on R1 “ip route 0.0.0.0 0.0.0.0 serial0/0″ will send any packet whose destination network is not referenced in the routing table of router R1 not R2…..//
@AVINASH – that’s correct, but what is your point?
Look at the previous post, then back at the router config.
The line “default-information originate” allows OSPF to share out a default route. This means that R2 learns about the default route and knows that to get to it, it must send packets to R1.
But R1 has the static route defined that sends packets to R2. But R2 has learnt of the default route at R1, but R1 has the default static route set to R2, but………………….
1- LSA type 1 : 3R3# sh ip ospf dsabaateLink ID ADV Router Age Seq# Checksum Link count2.2.2.2 2.2.2.2 1148 0 80000004 0x00778A 43.3.3.3 3.3.3.3 1326 0 80000003 0 000893 37.7.7.7 7.7.7.7 1141 0 80000004 0x00CB66 3net link : 1 -2Link ID ADV Router Age Seq# Checksum22.22.22.2 2.2.2.2 1147 0 80000001 0x00D7F1 R3#sh ip ospf dsabaate router 3.3.3.3 3 Link connected to: a Stub Network (Link ID) Network/subnet number: 3.3.3.3 (Link Data) Network Mask: 255.255.255.255 Number of TOS metrics: 0 TOS 0 Metrics: 1 Link connected to: another Router (point-to-point) (Link ID) Neighboring Router ID: 2.2.2.2 (Link Data) Router Interface address: 33.33.33.3 Number of TOS metrics: 0 TOS 0 Metrics: 64 Link connected to: a Stub Network (Link ID) Network/subnet number: 33.33.33.0 (Link Data) Network Mask: 255.255.255.0 Number of TOS metrics: 0 TOS 0 Metrics: 64R2#sh ip ospf dsabaate router 2.2.2.2 Link connected to: a Stub Network (Link ID) Network/subnet number: 2.2.2.2 (Link Data) Network Mask: 255.255.255.255 Number of TOS metrics: 0 TOS 0 Metrics: 1 Link connected to: another Router (point-to-point) (Link ID) Neighboring Router ID: 3.3.3.3 (Link Data) Router Interface address: 33.33.33.2 Number of TOS metrics: 0 TOS 0 Metrics: 64 Link connected to: a Stub Network (Link ID) Network/subnet number: 33.33.33.0 (Link Data) Network Mask: 255.255.255.0 Number of TOS metrics: 0 TOS 0 Metrics: 64R1#sh ip ospf dsabaate router 7.7.7.7Link connected to: a Stub Network (Link ID) Network/subnet number: 7.7.7.7 (Link Data) Network Mask: 255.255.255.255 Number of TOS metrics: 0 TOS 0 Metrics: 1 Link connected to: a Transit Network (Link ID) Designated Router address: 22.22.22.2 (Link Data) Router Interface address: 22.22.22.7 Number of TOS metrics: 0 TOS 0 Metrics: 10 Link connected to: a Stub Network (Link ID) Network/subnet number: 77.77.77.0 (Link Data) Network Mask: 255.255.255.0 Number of TOS metrics: 0 TOS 0 Metrics: 10
Reports officer, I was red tirlpe Huben reconnaissance unit soldiers. NM12MjBin Brother we eat this meal time can be long enough ah, huh, huh. Chao Having punched a burp, to meet the intoxicated with.Freeze, the Red Army scout. Disarray Li Bin, who broke into the headquarters of the Blues.Brothers, live, and you have killed, please follow the rules exercises. Having it with a towel Bin blue soldiers blocked the mouth. I put in the company commander to piled up together, this kid ran over the wall. Do not do, kind, Oh. We really destined, not you, ah, I do not know can not go home alive. Li Bin Having self-deprecating smile. Ruan Yunfei is one of them, as the Vietnamese military quiet to himself looking at the endless sea. Do not take three classes of people, I can, and company commander, political commissar, then I went to the Ha. Xu Biao Jing finished a military salute, turned and walked to the confinement. Brothers, live, and you have killed, please follow the rules exercises. Having it with a towel Bin blue soldiers blocked the mouth. Azb!MnJ Freeze, the Red Army scout. Disarray Li Bin, who broke into the headquarters of the Blues. I put in the company commander to piled up together, this kid ran over the wall. Reports officer, I was red tirlpe Huben reconnaissance unit soldiers.Do not do, kind, Oh. We really destined, not you, ah, I do not know can not go home alive. Li Bin Having self-deprecating smile. Ruan Yunfei is one of them, as the Vietnamese military burp, to meet the intoxicated with. Do not take three classes of people, I can, and company commander, political commissar, then I went to the Ha. Xu Biao Jing finished a military salute, turned and walked to the confinement.
i dnt understnd qtn no 6, can anyone help me on how it works?
ip route 0.0.0.0 0.0.0.0 serial0/0
this is setting s0/0 as the interface on which all packets should be send IF their destination is unknown to the router (the destination network is not in the routing table)
router ospf 1
enter configuration mode for the ospf process number 1. remember that the ospf process number is significant only for the router, not the for the area
network 172.16.100.0 0.0.0.3 area 0
advertise this subnet for area 0
network 172.16.100.64 0.0.0.63 area 0
advertise this subnet for area 0
network 172.16.100.128 0.0.0.31 area 0
advertise this subnet for area 0
default-information originate
advertise the default route to the other routers that are using OSPF within the same area.
the most important lines are the first and the last under the routing config mode.
the first one enables routing advertisements on the interface that connects to R2 (s0/0)
the last one redistributes the default route to other routers (s0/0 as a default route)
what will happen when R2 has a packet for an unknown destination?
R2 checks the routing table and sends the packet to R1 because it knows that R1 has a default route that should get that packet to its destination.
the packet arrives at R1, R1 checks the destination and sees that it is unknown to it too. R1 forwards the packet out the s0/0 interface because it is marked as the default route.
the s0/0 interface is the one that connects to R2 so R2 gets the packet back. R2 checks the destination, sends it to R1, R1 checks the destination, sends it to R2 and so on until the TTL (time to live) is exceeded. the TTL is 255 by default so the packet will do some 100 trips forth and back.
keep in mind that my example is about a single packet. during a second there are countless packets that could leave R2 towards unknown destinations…
what is that? a routing loop.
Hi Michael,I apologies if this is not the ccrerot place to ask questions!We have an ERS1600 and it has been getting the following error in the logs for some time without any apparent network impact: CPU1 [02/09/11 14:14:45] HAL WARNING NPAL_AddArp: could not create local host route 172.19.4.50 for ifindex -1 CPU1 [02/09/11 14:14:45] HAL WARNING NPAL_AddArp: could not create local host route 172.19.4.89 for ifindex -1 000: [02/09/11 14:14:42] The previous message repeated 1 time(s).However more recently, we had users reporting a loss in connectivity and looking at the logs they had changed: 24:0c301b5ba6d86884eb8c4c03e8fc79108adb874dcae8658e CPU1 [02/09/11 14:14:38] HAL WARNING NPAL_AddArp: could not create local host route 172.19.8.189 for ifindex 75 24:0c301b5ba6d86884eb8c4c03e8fc79108adb874dcae8658e CPU1 [02/09/11 14:14:37] HAL WARNING NPAL_AddArp: could not create local host route 172.19.4.45 for ifindex -1 000: [02/09/11 14:14:34] The previous message repeated 3 time(s).The long string has appears and the some kind of delimiting character? Have you seen this before and any idea of the cause?Kind Regards Matt
now I understand –q6 — it is the combo of static route and default information originate
so — now we have look out for the combo of a static route and default information originate???
Lol i cant believe the cenmomt saying it was intentional !I think the problem was caused by the introduction of static pages to blogger.Im using the bemagazine template and static pages appear in the summary box but the summary box can not be opened so basically i cant use static pages without some code changes.On the normal post pages i get the same navigation error as you guys, However when i set up a static page the navigation options appear perfectly on that page.I didnt even realise the error untill i seen this post, i have the navigation options at the bottom of the post as well as under the cenmomts so i will probably just remove the ones under the cenmomts.Check out the static pages and see if you also think thats the problem…Paul.
I’ve tried to set up this router 5 derfifent times. This time I tried it with this advice and it still didn’t work. I have a Trendnet router and I set it up using the wizard button clone MAC address . Nothin’. *sigh* The hunt continues for a way to have wireless and Roadrunner too.
These dumps are VERY accurate! If you know what you’re doing with Cisco equipment, and use these as practice questions you will pass your CCNA.
I passed my CCNA today with an 894. Good luck everyone!
I am taking my exam tomorrow and i am so nervous.
@ 9tut please remove the comment by Jibut its just chewing space for some important discussions, i dont see how it is related to CCNA. hey God help me
What are two drawbacks of implementing a link-state routing protocols? (Select two)
A. The large size of the topology table listing all advertised routes in the converged network
B. The sequencing and acknowledgement of link-state packets
C. The high demand on router resources to run the link-state routing algorithmn
D. The requirement for hierarchical IP addressing scheme for optimal functionality
E. The high volume of link-state advertisments in a converged network
I think answer is C, but what about second answer?
Regard to question 2
in order for two router to become neighbors the need to agree on :
- Hello and dead intervals
– Area ID (Area 0 in this case)
– Authentication password
– Stub area flag
- subnent mask
-MUT sized on connected interfaces
Hi all, I am taking CCNA 640-802 exam first time on 30/05/2012. Could anyone please send me latest dumps which are valid for UK? My e-mail address is puneet_gill84@yahoo.co.uk. Many thanks.
I agree with IT lady — remove comments that dont have anything to do with this site===
this site is a valuable tool for learning — thanks
Q5: B – Areas may be assigned any number from 0 to 65535 ?
can anyone explain this. if you check the router configuration is should be
Thansk
I PASSED CCNA EXAM TODAY THANKS TO ALL MIGHTY ALLAH
960/1000
xallax April 22nd, 2012 ip route 0.0.0.0 0.0.0.0 serial0/0
Quite Cool: REALLY Liked it Well-done[ Pls Keep-it-up]
Hi, Im Priya from Kerala(India).Im taking ccna exam on 30th June.Really im fed up.Can any one plz send me latest dumps to my email priya.ccna@yahoo.in Love you all .God Bless ..Thanks
priya
Hi about Q2.
Why is answer D correct? in the graphic all routers are in Area 0. I’ve noticed that is one of the most likely answers but may be a mistake there.
Sorry I was talking about answer C on Q6 not D
I find question 1: i find the answers should be C and D.
Which of the following statements below best describe the process identifier that is used to run OSPF on a router? (Choose two)
A – It is an optional parameter required only if multiple OSPF processes are running on the router
B – It is locally significant
C – It is needed to identify a unique instance of an OSPF database
D – All routers in the same OSPF area must have the same process ID if they are to exchange routing information
Please elaborate the answer and the conclusion to select B and C
Why the Q1 , D answer is not correct? I agree with @Zaya C and D.
What actually means “locally significant”? Within area? Within domain? I think it is not precisied enough