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OSPF Sim

January 8th, 2015 in Lab Sim, LabSim Go to comments

Question

OSPF is configured on routers Amani and Lynaic. Amani’s S0/0 interface and Lynaic’s S0/1 interface are in Area 0. Lynaic’s Loopback0 interface is in Area 2.

OSPFSim

Your task is to configure the following:

Portland’s S0/0 interface in Area 1
Amani’s S0/1 interface in Area 1
Use the appropriate mask such that ONLY Portland’s S0/0 and Amnani’s S0/1 could be in Area 1.
Area 1 should not receive any external or inter-area routes (except the default route).

Answer and Explanation:

First, we configure Portland’s S0/0 interface so that it belongs to Area 1. So, we have to find out which sub-network the IP address 192.168.4.5/30 (the IP of interface S0/0 of Portland) belongs to. This address belongs to a subnetwork which has:

Increment: 4 (/30 = 255.255.255.252 or 1111 1111.1111 1111.1111 1111.1111 1100)
Network address: 192.168.4.4 (because 4 = 4 * 1 and 4 < 5)
Broadcast address: 192.168.4.7 (because 7 = 4 + 4 – 1) (It is not necessary to find out the broadcast address but we should know it)

The question requires that only Portland’s S0/0 and Amani’s S0/1 could be in Area 1, therefore we must use a wildcard of 0.0.0.3 (this wildcard is equivalent with a subnet mask of /30) so that there are only 2 IP addresses can participate in area 1 (they are 192.168.4.5 & 192.168.4.6). The full command we use here is network 192.168.4.4 0.0.0.3 area 1

The question also requires that “Area 1 should not receive any external or inter-area routes (except the default route)”. Recall that if we don’t want the router to receive external routes, we have to stop LSA Type 5. And if we don’t want to receive inter-area routes, we have to stop LSA Type 3 and Type 4. Therefore we have to configure area 1 as a totally stubby area. For your information, here is the definition of a totally stubby area:

Totally stubb area – This area does not accept summary LSAs from other areas (types 3 or 4) or external summary LSAs (Type 5). Types 3,4 and 5 LSAs are replaced by the Area Border Router(ABR) with a default router. Totally stubby areas protect internal routers by minimizing the routing table and summarizing everything outside the area with a default route.” (CCNP BSCI Official Exam Certification Guide, Fourth Edition)

In conclusion, we have to configure area 1 as a totally stubby area. We do that by configuring Portland as stub and configuring Amani (ABR router) as a stub + “no-summary”suffix.

+ Configure Portland router as a stub:

Portland#configure terminal
Portland(config)#router ospf 1

Allow network 192.168.4.4/30 to join Area 1, notice that you have to convert subnet mask into wildcard mask:

Portland(config-router)#network 192.168.4.4 0.0.0.3 area 1

Configure Portland as a stub:

Portland(config-router)#area 1 stub

Portland(config-router)#end
Portland#copy running-config startup-config

+ Configure Amani router as a “totally stub”:

Amani#configure terminal
Amani(config)#router ospf 1
Amani(config-router)#network 192.168.4.4 0.0.0.3 area 1

Make area 1 become a totally stubby area, notice that we can only use this command on ABR router:

Amani(config-router)#area 1 stub no-summary

Amani(config-router)#end
Amani#copy running-config startup-config

Note: Make sure to check the OSPF process ID before typing your configuration. Maybe it is not OSPF process 1 like the configuration above.

 

Other lab-sims on this site:

EIGRP Stub Sim

EIGRP OSPF Redistribution Sim

IPv6 OSPF Virtual Link Sim

EIGRP Simlet
Policy Based Routing Sim

 

Comments
Comment pages
1 2 3 84
  1. Need
    December 19th, 2017

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  2. Mac
    December 20th, 2017

    @ bloomingonion

    Thanks for the information you provided it really help me figure out what’s going on with this lab. It says use the most specific wildcard mask possible, the key word is “POSSIBLE” I was using the specific wildcard mask for a /30 because you can’t get any more specific than that, not realizing that I need to use a (possible) wildcard mask that will allow pings to traverse the network and it doesn’t have to be absolutely SPECIFIC as I was thinking.

    Thanks again you may have saved my score with that piece of information.

  3. Mac
    December 20th, 2017

    Ok that wildcard mask is not longer working for me, I don’t know if its the lab or just the config but i’ll try it on the exam either way

  4. Dexter
    December 27th, 2017

    Mac, he is talking for Redistribution lab and you for OSPF

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    January 6th, 2018

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  7. User
    January 11th, 2018

    I was asked to create Area 2 and add Los Angles and Indianapolis routers and make them Stub Areas both with OSPF ID 75 on all the routers. Then I was asked I should be able to ping New York router loopback address 172.16.237.237 from Los Angles router.

    I configured Los Angles router as follow
    Router ospf 75
    Network 192.168.46.44 0.0.0.3 Area 2
    Area 2 Stub
    Copy Run St

    I configured Indianapolis as follow
    Network 192.168.46.44 0.0.0.3 Area 2
    Area 2 Stub no-Summary
    Copy Run St

    I was not able to ping loopback 0 or New York router. I used show Ip interface Brief on New York router only had serial interface configured. So no loopback 0 was configured, I tried to configure the loopback 0 172.16.237.237 on New York router the router would not let me do it when I tried config t was getting pop up “the configuration has been locked on this router”.

    Why Cisco asked me to ping a loopback address if it is not configured at all and why it would not let me add the loopback address which is missing to the New York router?

  8. v1pz
    January 12th, 2018

    To be honest you dont need to find out the wildcard mask.
    you can just to with the ip address on the interface and wildcard mask of 0.0.0.0
    It does the same thing activating the interface for hello messages.

  9. v1pz
    January 12th, 2018

    I guess this is an extra “cisco” question lol, in the real world I would never do that..

  10. ali
    January 13th, 2018

    can any one explain please how can we measure network ip ??

  11. Anonymous
    January 21st, 2018

    @User did you passed the exam

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    April 2nd, 2018

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  19. Elv
    April 16th, 2018

    Routers use different name. They are not exactly the same as the one’s in this site.

  20. Elv
    April 16th, 2018

    Routers use different names. They are not exactly the same as the one’s in this site.

  21. Elv
    April 16th, 2018

    But the overall solution is the same.

  22. unstoppable
    April 27th, 2018

    @Elv,

    whats the wildcard mask need to use?
    I don’t understand what people talking about the wildcard mask need to be in 0.0.0.7 for router Lynaic?

  23. 1w4n
    April 30th, 2018

    @unstopable not sure myself. Just labbed it in gns and loopback on Lynaic is pingable with wildcard mask of 0.0.0.3

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    June 3rd, 2018

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