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OSPF Evaluation Sim

February 9th, 2015 in Lab Sim Go to comments

You have been asked to evaluate an OSPF network and to answer questions a customer has about its operation. Note: You are not allowed to use the show running-config command.

OSPF.jpg

Although in this sim we are not allowed to use “show running-config” command but we post the configuration here so that you can understand more about the topology.

R1
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/0
ip address 192.168.13.1 255.255.255.0
ip ospf network non-broadcast
no shut
!
router ospf 1
network 192.168.13.0 0.0.0.255 area 0
network 1.1.1.1 0.0.0.0 area 0
R2
interface Loopback 0
ip address 2.2.2.2 255.255.255.255
!
interface S0/0
ip address 192.168.23.2 255.255.255.0
ip ospf network non-broadcast
no shut
!
router ospf 1
network 192.168.23.0 0.0.0.255 area 0
network 2.2.2.2 0.0.0.0 area 0
neighbor 192.168.23.3
R3
interface Loopback 0
ip address 3.3.3.3 255.255.255.255
!
interface Ethernet0/0
ip address 192.168.34.3 255.255.255.0
no shut
!
interface S1/0
ip address 192.168.23.3 255.255.255.0
ip ospf network non-broadcast
no shut
!
interface S1/1
ip address 192.168.13.3 255.255.255.0
ip ospf network non-broadcast
no shut
!
router ospf 1
network 192.168.13.0 0.0.0.255 area 0
network 192.168.23.0 0.0.0.255 area 0
network 192.168.34.0 0.0.0.255 area 1
network 3.3.3.3 0.0.0.0 area 0
area 1 virtual-link 4.4.4.4
neighbor 192.168.23.2
R4
interface Loopback 0
ip address 4.4.4.4 255.255.255.255
interface Ethernet0/0
ip address 192.168.34.4 255.255.255.0
no shut
!
interface Ethernet0/1
ip address 192.168.45.4 255.255.255.0
no shut
!
interface Ethernet0/2
ip address 192.168.46.4 255.255.255.0
no shut
!
router ospf 1
network 192.168.34.0 0.0.0.255 area 1
network 192.168.45.0 0.0.0.255 area 2
network 192.168.46.0 0.0.0.255 area 3
network 4.4.4.4 0.0.0.0 area 1
area 1 virtual-link 3.3.3.3
area 2 nssa
area 3 stub no-summary
R5
interface Loopback0
ip address 5.5.5.5 255.255.255.255
interface Loopback1
ip address 5.5.1.1 255.255.255.255
interface Loopback2
ip address 5.5.2.1 255.255.255.255
interface Loopback3
ip address 5.5.3.1 255.255.255.255
interface Loopback4
ip address 5.5.4.1 255.255.255.255
interface Ethernet0/0
ip address 192.168.45.5 255.255.255.0
no shut
!
router ospf 1
network 192.168.45.0 0.0.0.255 area 2
network 5.5.0.0 0.0.255.255 area 2
area 2 nssa
R6
interface Ethernet0/0
ip address 192.168.46.6 255.255.255.0
no shut
interface Loopback 0
ip address 6.6.6.6 255.255.255.255
!
router ospf 1
network 192.168.46.0 0.0.0.255 area 3
network 6.6.6.6 0.0.0.0 area 3
area 3 stub

Some notices from above configuration:

+ The OSPF network type between R2 & R3 is non broadcast.
+ R3 and R4 is running virtual-link to connect Area 2 & 3 to Area 0
+ Area 2 is a NSSA area while Area 3 is a Totally Stubby area

You can download this sim to practice at http://www.digitaltut.com/download/ROUTE_OSPF.zip. Please use GNS3 with version older than v1.0 to open it (v0.8.3.1 for example). IOS used in this lab: c3640-jk9s-mz.124-16.bin

Question 1

Explanation

To check OSPF LSA we should use the “show ip ospf database” command on R5:

R5_show_ip_ospf_database.jpg

In this sim there is no LSA Type 4 because there is no ASBR so maybe this question wants to ask about LSA Type 3 (Summary Net Link States).

Note: LSA Type 4 is generated by ABR, not ASBR but without ASBR inside the network there are no LSA Type 4 generated. For more information about OSPF LSA Types please read our OSPF LSA Types Lab tutorial.

R3 advertises LSA Type 1 to R4 then R4 converts it into Type 3 and sends to R5 (because R4 is the ABR) so we see the “Link ID” 3.3.3.3 of R3 is advertising by R4 (4.4.4.4). According to the “Age” column, this LSA was advertised 1858 seconds ago.

Question 2

Explanation

Check the Serial1/0 interface of R3 which is connected to R2 with the “show ip ospf interface serial 1/0” command:

R3_show_ip_ospf_interface_serial.jpg

There are two things we should notice from the output above:
+ The “network type” connection between R2-R3 is “NON_BROADCAST” (usually we have “BROADCAST”). OSPF neighbors are discovered using multicast Hello packets. In non broadcast environment, multicast (and broadcast) messages are not allowed so OSPF neighborship cannot be formed automatically. Therefore we have to establish OSPF neighborship manually by using “neighbor ” command under OSPF process (OSPF will send unicast Hello message to this address). For example on R2 we have to use these commands:

router ospf 1
neighbor 192.168.23.3

And on R3:

router ospf 1
neighbor 192.168.23.2

+ For non broadcast environment the default Hello timer is 30 seconds; Dead timer (time to wait before declaring a neighbor dead) is 120 seconds and Wait timer (causes the interface to exit out of the wait period and select a DR on a broadcast network. This timer is always equal to the dead timer interval) is 120 seconds. In the output we also see the default timers for non broadcast network.

Question 3

Explanation

We can check the number of executed SPF algorithm via the “show ip ospf” command on R4:

R4_show_ip_ospf.jpg

In the output above we can see SPF has been executed 9 times.

Question 4

Explanation

Area 2 (of R5) is a Not-so-Stubby area (NSSA). You can check it by the “show ip ospf” command on R4 or R5 (in Area 2 section). For example, below is the output of “show ip ospf” command on R5:

R5_show_ip_ospf.jpg

In general, NSSA is same as normal area except that it can generate LSA Type 7 (redistribute from another domain) so we can see both Loopback interfaces of R5 & R6 in the routing table of R5.

R5_show_ip_route.jpg

Note: NSSA does not receive a default route by default so you will not see a default route on R5.

Area 3 (of R6) is a Totally-Stubby area so R6 only has one default route to outside world. You can check with the “show ip ospf” command on R4 and R6 (area 3 section):

R4_show_ip_ospf_area3.jpg

R6_show_ip_ospf.jpg

Notice that on R4 you will get more detail (shows “stub area, no summary LSA”) than on R6 (only shows “stub area”).

R6 is in a totally-stubby area so we will not see any R5’s Loopback interfaces in R6 routing table:

R6_show_ip_route.jpg

Note: You can see a default (summary) route to the outside (O*IA 0.0.0.0/0 …)

Comments
Comment pages
1 6 7 8 1016
  1. Beagle
    March 26th, 2018

    If you miss one of the four questions on this simlet, do you fail the entire thing?

  2. Ricky
    March 28th, 2018

    Where are the questions?

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    March 30th, 2018

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  10. No pasaran
    May 1st, 2018

    Failed the test yesterday

    SIMS were OSPF/EIGRP evalutions and EIGRP stub .

    BUT there were so many questions I never see before !!!! .It was not funny :).

    I would say master all questions on this site .Listen/read/study as much material you can then you can pass the test .

  11. khaled
    May 8th, 2018

    i downloaded the same tutorial but got different details when i write this command ( show ip ospf database ) ..

  12. Csnavarro
    May 11th, 2018

    Hi Guys, I passed in routing exam today. The LAB are the same here, however in my exam there was a lot questions about Ipv6, NTP, SNMP, EVE none questions about OSPF and BGP.
    Two LABs PBR and EIGRP.

  13. Parsad
    May 12th, 2018

    Hi Guys, I want to ask, that if in OSPF evaluation lab in exam, you do not enter the commands on routers but your answers are correct ; then will you be awarded marks for your selection or not ??

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    May 23rd, 2018

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  27. Anonymous
    June 4th, 2018

    Q1: my explanation:
    So, we have to know that when an ASBR send a LSA type 1 to an ABR, the ASBR will flip just one bit to say, me I am ASBR,
    When an ABR received this kind of LSA, it will say to all other that this Router ID is an ASBR by creating a type 4 LSA and flooding it in its own area.
    This LSA type 4 will be flooded in all the other areas so that all routers in all areas will know where to find the ASBR.
    So the router R3 is supposed ASBR here, so this router will flip a bit to tell R4 that it is ASBR, and R4 will flood it to R5 an R6.
    The the line we have to check is the age of the R3 who is the creator of this LSA type 1 where it flipped one bit.
    All other responses are not okay

  28. RED1
    June 4th, 2018

    I answered to Q1 as anonymous but that’s me.

    Q2: This question is also a confusing question because, effectively we need to put the neighbor command to realise the adjacency simply cuz we are in a non-broadcast domain, so multicast of helos on the 224.0.0.5 and 224.0.0.6 are not performed, we can see it on the show ip ospf interface serial 1/0 command (the keyword broadcast)

    But in the other side timers 30, 120, 120 on the link R2-R3 is a good response.

    My opinion is that we dont need to put the command neighbor on R2 and R3 because the adjacency is done yet, we can see it on the line : neighbor count is 1, adjacent neighbor count is 1
    so I suppose that this task to put the neighbor command is done yet and we dont need to put it another time.

    This is a confused question but it is my opinion.

    :)

  29. RED1
    June 5th, 2018

    Q1. I have put the sim on GNS3.
    question: How old is the type 4 LSA from Router 3 for area 1 on the router R5 based on the output you have examined?
    So:
    On the router 3 when ask for the ospf database: show ip ospf database asbr-summary
    we see that R3 with router ID 3.3.3.3 is the advertiser of two asbr-summary LSAs, one concerning area 0 and the other concerns area 1, and the question was asked to chek the LSA wich concerns area 1
    it is this one:
    Summary ASB Link States (Area 1)
    LS Type: Summary Links(AS Boundary Router)
    Link State ID: 4.4.4.4 (AS Boundary Router address)
    Advertising Router: 3.3.3.3

    we have to look at the 4.4.4.4 age on router R5,

    This is my comprehention and I think that the good response is 1858 according to the output show on the response on dumps.

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  33. mujib
    June 18th, 2018

    Hi Everyone,

    Can any one please explain why on question 2, we use sh ip ospf interface s1/0 though we have another serail inteface s1/1

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    June 20th, 2018

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  35. SG
    June 21st, 2018

    @mujib
    sh ip ospf interface would also help. In this question we are trying to see the Hello and Dead timer values for each interface.

  36. mujib
    June 21st, 2018

    Hi

    On ospf question 2 on router3 there are two interfaces, then why we use only show ip ospf interface serial 1/0, and why not serial interface s1/1.
    Can Anybody Explain please

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