OSPF Questions 3
Here you will find answers to OSPF Questions – Part 3
Question 1
Refer to the exhibit. You are the network administrator responsible for the NProuter, the 10.1.1.1 router, and the 10.1.1.2 router. What can you determine about the OSPF operations from the debug output?
|
NProuter#debug ip ospf events OSPF events debugging is on NProuter# |
A. The NProuter has two OSPF neighbors in the “Full” adjacency state.
B. The NProuter serial0/0 interface has the OSPF dead timer set to 10 seconds.
C. The NProuter serial0/0 interface has been configured with an OSPF network type of “point-to-point”.
D. The 10.1.1.1 and 10.1.1.2 routers are not using the default OSPF dead and hello timers setting.
E. The “Mismatched” error is caused by the expiration of the OSPF timers.
Answer: B
Explanation
First we should understand clearly about the line
Dead R 120 C 10, Hello R 30 C 30
The “R” here means “Received” and “C” means “Configured”. In other words, “Dead R” is the Dead Timer Received from the neighbor and the “Dead C” is the Dead Timer of the local router.
Therefore in this case “Dead R 120 C 10″ means the Death Timer of the neighbor is 120 seconds while the local Dead Timer is 10 seconds, which causes a mismatch. Also we can learn that the local OSPF dead timer is set to 10 seconds -> B is correct.
For your information, by default, OSPF uses a 10-second hello timer and 40-second hold timer on broadcast and point-to-point links, and a 30-second hello timer and 120-second hold timer for all other network types. So we can’t confirm answer D is correct or not.
Question 2
You have just completed an OSPF implementation. While executing your verification plan, you determine that R1 is not able to establish full OSPF adjacency with R2. The show ip ospf neighbor command output on R1 shows that R2 is stuck in the INIT state.
What could be the cause of this problem?
A. DR and BDR election errors between R1 and R2.
B. The R2 router has not received the OSPF hello packets from the R1 router.
C. Mismatched interface maximum transmission unit (MTU) configuration between the R1 and R2.
D. Mismatched OSPF hello interval configuration between the R1 and R2.
E. Corrupted LSAs exchanges between the R1 and R2.
Answer: B
Explanation
When a router receives an OSPF Hello from a neighbor, it sends the Hello packet by including that neighbor’s router ID in the Hello packet. If the neighbor does not receive this packet (means that it doesn’t see itself in this packet), it will be stuck in INIT state. INIT state can be understood as a one-way Hello. An example of a router stuck in INIT state is shown below:
Question 3
Refer to the exhibit. You have completed an OSPF implementation, and you are verifying OSPF operation. You notice that router A and router B are stuck in the two-way state. From the show ip ospf interface command output, what is the cause of this issue?
A. All OSPF implementations must have at least one interface in area 0.
B. You are attempting to run in the broadcast mode over an NBMA interface.
C. Both routers are configured to function as a BDR; therefore, there is no DR router.
D. Someone has changed the OSPF router ID; therefore you must clear the OSPF process.
E. The OSPF priority is set to 0 on both routers; therefore neither can become the DR.
Answer: E
Explanation
When OSPF adjacency is formed, a router goes through several state changes before it becomes fully adjacent with its neighbor. The states are Down, Attempt, Init, 2-Way, Exstart, Exchange, Loading, and Full.
An OSPF neighbor reaches the 2-way state when bidirectional communication is established (each router has seen the other’s hello packet). This is the beginning of an OSPF adjacency. On broadcast media and non-broadcast multiaccess networks, the DR and BDR are elected in this state. But the priority on both routers are 0 so no DR and BDR are elected -> These routers stay in the 2-way state.
(Reference and a good resource of OSPF Neighbor states: http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080093f0e.shtml)
Question 4
You have completed an OSPF implementation, and you are verifying OSPF operation. During this verification, you notice that the OSPF route of 172.16.10.0 is repeatedly appearing and disappearing from the routing table. Further investigation finds that the OSPF CPU utilization is very high and the routers are constantly performing SPF calculations. You determine that 172.16.20.2 is the source of the 172.16.10.0 route. Using the show ip ospf database router 172.16.20.1 command, you notice that when this show command is performed repeatedly, the contents of the LSA change every few seconds.
What could be the cause of this problem?
A. OSPF authentication errors between some of the routers.
B. Two routers have the same OSPF router ID.
C. Issues with mistuned OSPF timers.
D. OSPF LSA pacing issues between some of the routers.
E. OSPF neighbor adjacency problems between some of the routers.
Answer: B
Question 5
The maximum number of routers per OSPF area typically depends on which three factors? (Choose three)
A. the kind of OSPF areas being implemented
B. the number of external LSAs in the network
C. the number of DRs and BDRs in the areas
D. the number of virtual links in the areas
E. how well the areas can be summarized
F. the use of LSA filters
Answer: A B E
Question 6
When verifying OSPF virtual link problems, which is an important item to check on the two transit OSPF routers?
A. OSPF process ID
B. OSPF router ID
C. OSPF network type
D. OSPF memory usage
E. OSPF CPU utilization
F. OSPF stub area configurations
Answer: B
Explanation
The OSPF router IDs of the two transit OSPF routers are used to form the virtual link (with the area area-id virtual-link neighbor-router-id command) so it is an important item to check -> B is correct.
Question 7
The administrator wants to verify the current state of the OSPF database loading process.
Which show command should the administrator use?
A. show ip ospf [process-id] interface
B. show ip ospf neighbor
C. show ip ospf [process-id]
D. show ip ospf [process-id area-id] database
Answer: B
Explanation
The “show ip ospf neighbor” command can be used to view the current state of the OSPF database loading process. In the output below we can see router 2.2.2.2 is in 2way state, router 3.3.3.3 is elected as the BDR & router 4.4.4.4 is the BR.
Question 8
Which two statements about route redistribution when implementing OSPF are true? (Choose two)
A. Routes learned using any IP routing protocol can only be redistributed into non IP routing protocols.
B. OSPF can import routes learned using EIGRP, RIP, and IS-IS.
C. OSPF routes cannot be exported into EIGRP, RIP, and IS-IS.
D. At the interdomain level, OSPF cannot import routes learned using BGP.
E. OSPF routes can be exported into BGP.
Answer: B E
Question 9
An administrator types in the command router ospf 1 and receives the error message: “OSPF process 1 cannot start.” (Output is omitted.)
What should be done to correctly set up OSPF?
A. Ensure that an interface has been configured with an IP address.
B. Ensure that an interface has been configured with an IP address and is up.
C. Ensure that IP classless is enabled.
D. Ensure that the interfaces can ping their directly connected neighbors.
Answer: B
Explanation
OSPF can be only started when there is at least one interface up and configured with an IP address on the router.
Question 10
Which three are advantages to creating multiple areas in OSPF? (Choose three)
A. less frequent SPF calculations
B. fewer hello packets
C. smaller routing tables
D. reduced LSU overhead
E. fewer adjacencies needed
Answer: A C D
Explanation
OSPF routers within an area only need to know about other routers within their own area, not outside their area, and all OSPF routers within a given area share the same link state database. This keeps the routing tables small enough to prevent processing bottlenecks from occurring -> C is correct.
Also SPF only needs to calculate paths to routers within that area -> A is correct.
If a router receives an LSA with old information then it will send a LSU to the sender to update the sender with the newer information. The Link State Update (LSU) holds the LSAs. Instead of sending multiple LSUs the ABR / ASBR summarizes a route and sends only one LSU-> D is correct.
Note: The LSA has a 30 minute timer that causes the router to send an LSU to everyone on the network once it ages out.
Hello Friends,
I just started to study the ROUTE test after taking almost two years off from passing the CCNA. I am planning to take the ROUTE test in two months. Are the Sims, Drag and Drop, Questions, and everything else on this site still valid for the ROUTE test?
Thank you all!
I guess the correct answer for q2 should be D as per Jeremy’s Video because R2 would be in INIT state when receives a hello from R1.
Then the criteria of the hello packet information is compared before it sends a reply hello and enters 2 way state..
Now since it is stuck in INIT state that means that one of hello criteria(parameter) i.e Hello interval sent by R1 is not matching with R2….
Kindly correct me if I am wrong…
@Anonymous.
I thought it also but if You rember they will never become neighbors if they have a hello and dead interval mismatch, so there is NO ospf adjacency.
I hope this helped You ;)
Are these questions still the most uptodate?
I dint get How the answer for question 4 is B
@Ramya
This situation can be achieved if you have 3 routers and triangle sceme
R1——–R2
\ /
\ /
R3
R1 and R2 have the same RID but will not become neighbors, and R3 have 2 neighbors with the same RID. High cpu load, SPF recalculations and the contents of the LSA change every few seconds will be on R3.
@Ramya
This situation can be achieved if you have 3 routers and triangle sceme
R1——–R2
\ /
\ /
R3
R1 and R2 have the same RID but will not become neighbors, and R3 have 2 neighbors with the same RID. High cpu load, SPF recalculations and the contents of the LSA change every few seconds will be on R3.
R1 and R2 connect to R3
Question2:
Should the answer not be:
D. Mismatched OSPF hello interval configuration between the R1 and R2.
The init state is a permanent state when Hello Parameters do not match:
When a router is waiting for the other Router’s Hello it is in Attempt state.
Attempt:
Used when the neighbor is defined with the neighbor command, after sending Hello, but before receiving a Hello from that neighbor
INIT:
A hello has been received from that neighbor, but it did not have the local router’s RID in it or lists parameters that do not pass the neighbor verification checks, this is a permanent state when Hello parameters do not match.
And so Answer B seems to be wrong.
Am i missing something?
From my best understanding CBT Nuggets videos of Jeremy, I believe that correct answer for Question 2 is B.
Sorry, I mean correct answer is D (mismatched hello parameters). Sorry for confusion.
Can anyone explain answers of Q5, why they are A, B, E? How about F? Thanks!
I dont understand Q4. I think when u have 2 router with the same RID . the router are neighbors but no exchange router… is correct?
@Digitaltut
For question 4, if the Router-IDs are same on both ends, the adjacency would never form.
I tried this in the lab, and get the following error.
%OSPF-4-DUP_RTRID_NBR: OSPF detected duplicate router-id 2.2.2.2 from 10.1.1.2 on interface FastEthernet0/0
Can’t the frequent route flaps be due to mistuned OSPF timers?
Appreciate your comments on this.
Thanks
Mikey
I also think that q2 must be B and this why.
When a router receives a hellos from a neighbor its go into INIT state and then starts to check to these parameters:
hello/dead interval
netmaks
Area ID
(optional) Authentication
If when of these not match it stays in INIT state.
Answer B states that R2 didn’t received a hello from R1 which is not true otherwise it would be in a down state
Sorry i ment Answer D excuses me
For Q2, check out this link: http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080093f11.shtml
Explains why the answer is B. My thoughts on why D isn’t right is that if the timers are mismatched then the state goes to DOWN and you don’t even see anything in “show ip ospf neighbor”. I tested this in a lab as well. Correct me if I’m wrong on any of this.
a helpful link for Q2:
http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080093f0e.shtml
Hi Mikey, I came to the same conclusion as you but then I found this on Cisco’s website:
http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080117102.shtml
About Question 2: Looking at pages 158 and 197 in the CCNP ROUTE Official Certification Guide by Wendell Odom, isn’t the correct answer to actually C – Mismatched interface maximum transmission unit (MTU) configuration between the R1 and R2?
Question 4 needs to be explained…
Question 5: Why not F?
Saw now that Q4 is actually explained in Louie’s link. (Thanks!)
Question 5: Why F is not correct? Can someone help?
Q2, another way to explain it:
R1 is initially in state DOWN
R1 receives a vanilla hello from R2, it’s gone to INIT and sent a hello with R2s ID included.
R2 has NOT responded with a hello that includes R1s ID in it. Just another vanilla hello.
R1 is therefore stuck in INIT having seen a vanilla hello from R2 that has not got it’s ID in it, responded with an R2 ID loaded hello in receipt and now only gets vanilla hellos from R2 again.. and again …etc
transport R2>>R1 obviously works as R1 is in INIT with a reference to R2.
R2 equally obviously receives no hellos from R1 or it would put R1s ID in a hello and send to R1 on the segment.
The question appears to be challenging as it states R2 is stuck in INIT.
Could be more to the point to say R1s knowledge of it’s relationship with R2 is stuck in INIT, we don’t know what the state of R2 is as we are only considering output from R1s console that references the state of R1 but we do know R2 is not in INIT because it’s not responding with a neighbour ID included on this segment.
Answer B makes sense to me although originally reading it I was confused by the reference to R2s INIT state.
Q2
C is false because with mtu mismatch R2 can reach exstart state and moves to down and so on.
You can read Example 5-6 Setting IP MTU and Failing the OSPF Database Exchange Process in Official Certification Guide, for a more detailed explanation.
B is false because if R2 hasn’s yet received a hello from R1, R2 will be in down or attempt state.
I think answer D is right because init is a permanent state when hello parameters do not match.
Q3
E is not reasonable. in point to point connection, there is no DR or BDR. Hence the answer doesn’t make sense.
Q3
However in Configuration, We can see the Network type is Broadcast! Is it the cisco feature for NBMA networks?
For question , B is correct:
I agree with JP and below link give proof for same
http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080093f11.shtml
Below is my explaination based on adjacency formation step by step.
1)R1 is in down state. All connected interface(Here R2 & R1) start neighbor discovery by sending hello packet on multicast address 224.0.0.5.
2)R1 receive hello packet from R2 and add R2 to list of neighbors. This state is init state.
3)R1 that received hello packets should send a unicast reply to R2 with reply hello packet (with RID, timers and other parameters).
4)R2 once receive the hello packets will check its own RID and other parameters. If all mandatory parameters match then R1 goes to 2 way state.
If any thing goes wrong it should be at step 3 or 4. Lets assume that R2 has successfully received hello packet from R2 and it founds hello timers mismatch then the state will change from INIT to DOWN.The question says the R2 neighbor ship stuck in INIT state.
Thus D cannot be correct as state is INIT.
It also means the reply hello packet from R1 lost somewhere due to reasons provided in above link.
Hope this help.
Above explaination is for Question 2
For question 3, E is correct
In show output state show DROTHER and interface type Non broadcast. DR /BDR are elected in Non brodcast type
OSPF Network Types Interface Type Uses DR/BDR? Compliant mode
Broadcast Yes Cisco
Point-to-point1 No Cisco
Nonbroadcast2 (NBMA) Yes RFC
Point-to-multipoint No RFC
“Point-to-multipoint NO Ciscso
nonbroadcast”
Correction In question 3 interface type is broadcast which requires DR/BDR to elected
@Viki Question 2
i think correct answer is D
According to OOfical certification Guide from Cisco
Init :
A Hello has been received from the neighbor, but it did not have the local router’s
RID in it or lists parameters that do not pass the neighbor verification checks. This
is a permanent state when Hello parameters do not match.
page 197
@Viki Question 2
btw i check your cisco resources and found your answer C is correct from their prespective
i think the Cisco Official certification Guide is wrong since the site will be more trusted source than this stupid Guide
OOOOOooooohhhh Cisco why WHY WHY
Q4… http://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a0080094e9e.shtml#t40
sorry, the above link answers Q5, not Q4.
hello frnds after reading all your comment i just search for the Q2 detail and i found sum of the details.First of all init is the one way step.when a router send a hello packet to another router then the another router first check its router id in that hello packet and therafter the remaining parameter.Now if the router id is not found it will become stay in init,& if it finds the router id then it will check the other parameter.if it mismatch then still stay in init state but the first preference always go to the router id since router first checks its router id then the remaining parameter.I found this detail on page no 197 of ccnp route by wendell odom,& even checked the link
http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080117102.shtml
on cisco so i think the ans is rite….correct me if i am wrong
In question 1, why is C not an answer? I see a serial interface and think it should be a point to point.
A litle confuse by question #2
Stuck in the INIT means the router had received something, but the router id was not in that message. So, ans B is not correct. I would have guessed D instead. Nothing seems to be correct. Anyone?
Q2:
Init : A Hello has been received from the neighbor, but it did not have the local router’s RID in it. (cisco press book)
i think the B is correct answer
Q10.
Answer C is not exactly correct.
Multiple areas do not decrease the size of the routing table as all the prefixes in the OSPF domain do exist in a non-backbone “regular” area or in the backbone area.
Eventually in a totally stubby area some prefixes will be not present because they will be “replaced” by a default route. Or we can also consider that areas allow summarization (on the ABR) and can thus reduce the routing table size. But these are special cases.
The real impact of having mutliple areas is reducing the size of the LSDB!
@Pedro,
Well, if all routers are in one area, each will have to know about other routers in that area – but, when they are split, each needs to know about the routers in its area and a path to the others. That is a very significant reduction.
What is the difference between LSA and LSU and when they are generated
look at
http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080093f11.shtml
router2#show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
170.170.5.1 1 INIT/- 00:00:34 170.170.1.1 Serial0
router-2#
In this example output, the init state indicates that router-2 sees hello packets from the neighbor, but two-way communication has not been established.
…
In other words, a router with a neighbor in the init state has received hello packets from the neighbor but has not seen its own Router ID in the neighbor’s hellos.
…
The most likely reason that a local router is not listed in a neighbor’s hello packets is that the neighbor has not received hello packets from the local router.
Q2 and Q10 were on my exam today.
@DigitalTUT
Q1) It should be D, as by default in Cisco dead interval is 4*hello Interval. So clearly in this case they are not using the default values.
Q4: The answer should be:
C. Issues with mistuned OSPF timers.
Nothing stops you in configuring :
Router(config-if)#ip ospf hello-interval 10
Router(config-if)#ip ospf dead
Router(config-if)#ip ospf dead-interval 5
Router(config-if)#^Z
This is what happens :
*Mar 1 00:18:45.515: %OSPF-5-ADJCHG: Process 1, Nbr 3.3.3.3 on FastEthernet0/0 from FULL to DOWN, Neighbor Down: Dead timer expired
*Mar 1 00:18:50.423: %OSPF-5-ADJCHG: Process 1, Nbr 3.3.3.3 on FastEthernet0/0 from LOADING to FULL, Loading Done
*Mar 1 00:19:05.995: %OSPF-5-ADJCHG: Process 1, Nbr 3.3.3.3 on FastEthernet0/0 from FULL to DOWN, Neighbor Down: Dead timer expired
*Mar 1 00:19:10.423: %OSPF-5-ADJCHG: Process 1, Nbr 3.3.3.3 on FastEthernet0/0 from LOADING to FULL, Loading Done
*Mar 1 00:19:23.247: %OSPF-5-ADJCHG: Process 1, Nbr 3.3.3.3 on FastEthernet0/0 from FULL to DOWN, Neighbor Down: Dead timer expired
When using the same router ID, Cisco IOS provides an error message and the adjacency will not form.
Flip
plz add topology of this question to can imagine it
@Q-6
I understand (B) is not wrong but why is (F) wrong…Virtual links cannot be configured with stubby-transit areas, if i know correctly, so that makes (F) also a valid choice or am I missing something guys!?
@ Scooby
By definition, a stub is only connected to one area. If it is connected to two or more areas, it is no longer a stub..it is a transit area, which can potentially have a virtual link in it, if necessary. If I picture in my head a stub, I cant see how I could bring up a virtual link to another area if the said stub is only connected to one area.
@ Above
Thanks for the reply but I got the reason and it’s not that a stub area cannot be connected as a transit area b/w two areas – configuring so will not give any errors but when you try to create a VL across it, router will reject it right away so no case of t/shootin’ or “verifying” the VL issue as no VL will be there!! But if wrong RID is used while configuring, no error/warning will be given but the created VL will not work- will require t-shoot/verification. So (B) is apt here. Clever use of words by CISCO.
And Digitaltut….RESPECT!!
Question 7
The administrator wants to verify the current state of the OSPF database LOADING process.
B. show ip ospf neighbor
Explanation
The “show ip ospf neighbor” command can be used to view the current state of the OSPF database loading process.
———–
on route guide it says:
Loading: Exchange of LSRs and LSUs, to populate LSDBs.
what does neighborship has to do with database loading state? anyone sees LSRs and LSUs exhange O_o?
Bona fide camaraderie foresees the requirements of extra versus promulgate it can be personal. casquette ymcmb http://www.c33.fr/
Q7 was on my exam today, solution is ok.
@Q7:
State: “FULL/DR” in the output
FULL (or any other state) is the loading state. Solution is valid.