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CCNA Training » OSPF Neighbor Sim

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October 6th, 2014 Go to comments Question Refer to the topology. topology. Your company has decided to connect conn ect the main office with three other remote branch offices using point-to-point serial links. You are required to troubleshoot and resolve OSPF neighbor adjacency issues between the main office and the routers located in the remote branch offices.

Instead of posting the output of “show run” commands we w e post here the commands entered on each router to reduce some useless lines. Also you can try solving s olving questions by yourself before reading the answers.

R1 interface Loopback0

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R2

R3

!

username R6 password

interface Loopback0

CISCO36

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CCNA Training » OSPF Neighbor Sim

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! interface Loopback0  description **Loopback**  ip address 192.168.3.3 255.255.255.255  ip ospf 3 area 0 !

 description ***Loopback***  ip address 192.168.1.1

 description **Loopback**

interface Ethernet0/0

255.255.255.255

 ip address 192.168.2.2

 description **Connected to

 ip ospf 1 area 0

255.255.255.255

L2SW**

!

 ip ospf 2 area 0

 ip address 10.10.230.3

interface Ethernet0/0

!

255.255.255.0

 description **Connected to

interface Ethernet0/0

 ip ospf 3 area 0

R1-LAN**

 description **Connected to

!

 ip address 10.10.110.1

R2-LAN**

interface Serial1/0

255.255.255.0

 ip address 10.10.120.1

 description **Connected to

 ip ospf 1 area 0

255.255.255.0

R4-Branch1 office**

!

 ip ospf 2 area 0

 ip address 10.10.240.1

interface Ethernet0/1

!

255.255.255.252

 description **Connected to

interface Ethernet0/1

 encapsulation ppp

L2SW**

 description **Connected to

 ip ospf 3 area 0

 ip address 10.10.230.1

L2SW**

!

255.255.255.0

 ip address 10.10.230.2

interface Serial1/1

 ip ospf hello-interval 25

255.255.255.0

 description **Connected to

 ip ospf 1 area 0

 ip ospf 2 area 0

R5-Branch2 office**

!

!

 ip address 10.10.240.5

router ospf 1

router ospf 2

255.255.255.252

 log-adjacency-changes

 log-adjacency-changes

 encapsulation ppp  ip ospf hello-interval 50  ip ospf 3 area 0 ! interface Serial1/2  description **Connected to R6-Branch3 office**

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CCNA Training » OSPF Neighbor Sim

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 ip address 10.10.240.9 255.255.255.252  encapsulation ppp  ip ospf 3 area 0  ppp authentication chap ! router ospf 3  router-id 192.168.3.3 ! R6 R4

R5

!

!

interface Loopback0

interface Loopback0

 description **Loopback**

 description **Loopback**

 ip address 192.168.4.4

 ip address 192.168.5.5

255.255.255.255

255.255.255.255

 ip ospf 4 area 2

 ip ospf 5 area 0

!

!

interface Ethernet0/0

interface Ethernet0/0

 ip address 172.16.113.1

 ip address 172.16.114.1

255.255.255.0

255.255.255.0

 ip ospf 4 area 2

 ip ospf 5 area 0

!

!

interface Serial1/0

interface Serial1/0

 description **Connected to

 description **Connected to

R3-Main Branch office**

R3-Main Branch office**

 ip address 10.10.240.2

 ip address 10.10.240.6

255.255.255.252

255.255.255.252

 encapsulation ppp

 encapsulation ppp

 ip ospf 4 area 2

 ip ospf 5 area 0

!

!

router ospf 4

router ospf 5

 log-adjacency-changes

 log-adjacency-changes

username R3 password CISCO36 ! interface Loopback0  description **Loopback**  ip address 192.168.6.6 255.255.255.255  ip ospf 6 area 0 ! interface Ethernet0/0  ip address 172.16.115.1 255.255.255.0  ip ospf 6 area 0 ! interface Serial1/0  description **Connected to R3-Main Branch office**  ip address 10.10.240.10 255.255.255.252  encapsulation ppp  ip ospf 6 area 0  ppp authentication chap ! router ospf 6

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CCNA Training » OSPF Neighbor Sim

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 router-id 192.168.3.3 ! Question 1  An OSPF neighbor adjacency is not formed between R3 in the main office and R4 in the Branch1 office. What is causing the problem?  A. There is an area ID mismatch. B. There is a Layer 2 issue; an encapsulation mismatch on serial links. C. There is an OSPF hello and dead interval mismatch. D. The R3 router ID is configured on R4.

 Answer: A  Explanation We learned it is a OSPF problem so we should check the interfaces between them first. On both R3 and R4 use “show running-config” command to check their S1/0 interfaces

! interface Serial1/0 description **Connected to R4-Branch1 office** ip address 10.10.240.1 255.255.255.252 encapsulation ppp ip ospf 3 area 0 ! R4 ! interface Serial1/0 description **Connected to R3-Main Branch office**

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CCNA Training » OSPF Neighbor Sim

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ip address 10.10.240.2 255.255.255.252 encapsulation ppp ip ospf 4 area 2 ! In the output above we see their Area IDs are mismatched; interface S1/0 of R3 is in area 0 (R3: ) while interface s1/0 of R4 is in area 2 (R4:

).

Question 2  An OSPF neighbor adjacency is not formed between R3 in the main office and R5 in the Branch2 office. What is causing the problem?  A. There is an area ID mismatch. B. There is a PPP authentication issue; a password mismatch. C. There is an OSPF hello and dead interval mismatch. D. There is a missing network command in the OSPF process on R5.

 Answer: C Explanation Continue checking their connected interfaces with the “show running-config” command:

! interface Serial1/1 description **Connected to R5-Branch2 office** ip address 10.10.240.5 255.255.255.252 encapsulation ppp ip ospf hello-interval 50 ip ospf 3 area 0 !

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CCNA Training » OSPF Neighbor Sim

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! interface Serial1/0 description **Connected to R3-Main Branch office** ip address 10.10.240.6 255.255.255.252 encapsulation ppp ip ospf 5 area 0 ! The only difference we can see here is the line “ip ospf hello-interval 50  on R3. This command ″

sets the number of seconds R3 waits before sending the next hello packet out this interface. In this case after configuring this command, R3 will send hello packets to R5 every 50 seconds. But the default value of hello-interval is 10 seconds and R5 is using it. Therefore we can think of a hello interval mismatch problem here. You can verify with the “show i p ospf interface ”  command on each router.

Serial1/1 is up, line protocol is up Internet Address 10.10.240.5/30, Area 0 Process ID 3, Router ID 192.168.3.3, Network Type POINT_TO_POINT, Cost: 64 Enabled by interface config, including secondary ip addresses Transmit Delay is 1 sec, State POINT_TO_POINT, Timer intervals configured, Hello 50, Dead 200, Wait 200, Retransmit 5 oob-resync timeout 200 Hello due in 00:00:28 Supports Link-local Signaling (LLS) Index 2/2, flood queue length 0 Next 0×0(0)/0×0(0) Last flood scan length is 0, maximum is 0 Last flood scan time is 0 msec, maximum is 0 msec Neighbor Count is 0, Adjacent neighbor count is 0 Suppress hello for 0 neighbor(s)

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CCNA Training » OSPF Neighbor Sim

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Serial1/0 is up, line protocol is up Internet Address 10.10.240.6/30, Area 0 Process ID 5, Router ID 10.10.240.6, Network Type POINT_TO_POINT, Cost: 64 Enabled by interface config, including secondary ip addresses Transmit Delay is 1 sec, State POINT_TO_POINT, Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5 oob-resync timeout 40 Hello due in 00:00:04 Supports Link-local Signaling (LLS) Index 1/1, flood queue length 0 Next 0×0(0)/0×0(0) Last flood scan length is 0, maximum is 0 Last flood scan time is 0 msec, maximum is 0 msec Neighbor Count is 0, Adjacent neighbor count is 0 Suppress hello for 0 neighbor(s) So we can see both hello and dead interval are mismatched because the dead interval always four times the value of hello interval, unless you manually configure the dead interval (with the command). Question 3 R1 does not form an OSPF neighbor adjacency with R2. Which option would fix the issue?  A. R1 ethernet0/1 is shutdown. Configure no shutdown command. B. R1 ethernet0/1 configured with a non-default OSPF hello interval of 25; configure no ip o spf  hello-interval 25 C. R2 ethernet0/1 and R3 ethernet0/0 are configured with a non-default OSPF hello interval of 25 ; configure no ip ospf hello-interval 25 D. Enable OSPF for R1 ethernet0/1; configure ip ospf 1 area 0 command under ethernet0/1  Answer: B Explanation Continue checking their connected interfaces with the “show running-config” command:

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! interface Ethernet0/1 description **Connected to L2SW** ip address 10.10.230.1 255.255.255.0 ip ospf hello-interval 25 ip ospf 1 area 0 !

! interface Ethernet0/1 description **Connected to L2SW** ip address 10.10.230.2 255.255.255.0 ip ospf 2 area 0 ! We see the hello interval on R1 is not the same as R2 (and you can verify with the “show ip ospf  interface command”) -> There is a hello and dead interval mismatch problem. We should configure “no ip ospf hello-interval 25  on R1. ″

Note: Maybe there are some versions of this question in the exam. For example there are some reports saying that Ethernet0/1 on R1 is shutdown (and this is the correct choice in the exam). So please be careful checking the config on the routers before choosing the correct answers. Question 4  An OSPF neighbor adjacency is not formed between R3 in the main office and R6 in the Branch3 office. What is causing the problem?  A. There is an area ID mismatch. B. There is a PPP authentication issue; the username is not configured on R3 and R6. C. There is an OSPF hello and dead interval mismatch.

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D. The R3 router ID is configured on R6.

 Answer: D Explanation

username R6 password CISCO36 ! interface Serial1/2 description **Connected to R6-Branch3 office** ip address 10.10.240.9 255.255.255.252 encapsulation ppp ip ospf 3 area 0 ppp authentication chap ! ! router ospf 3 router-id 192.168.3.3 !

username R3 password CISCO36 ! interface Serial1/0 description **Connected to R3-Main Branch office** ip address 10.10.240.10 255.255.255.252 encapsulation ppp ip ospf 6 area 0 ppp authentication chap !

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CCNA Training » OSPF Neighbor Sim

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! router ospf 6 router-id 192.168.3.3 ! We are not sure about the configuration of ppp authentication in this case. Some reports said th at only one router has the “ppp authentication chap” command but it is just a trick and is not the problem here. The real problem here is R6 uses the same router-id of R3 (192.168.3.3) so OSPF neighborship cannot be established. In real life, such configuration error will be shown in the command line interface (CLI). So please check carefully for this question. Comments (102) Comments Comment pages « Previous 1 2 3 2243 1. Omz November 23rd, 2014 Oppps … omc79 at hotmail dot com 2. lonn November 24th, 2014 no .pka to download of this section ? Comment pages « Previous 1 2 3 2243  Add a Comment  Name

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