lab 3, task 4.8 ospf loopback advertisement

Hi All,

Im just wondering about this answer for the part of Area 3 range 150.1.3.0 255.255.255.0.

in the question on 3rd bullet of task 4.8  says this network should be associated with an ospf area. but it did not mentioned area 3 thats why im confuse why is there an area 3 in ans which in diagram it is clearly wrote area 34. is this the correct ans or just a typo instead of 34 only 3 was written.

 

R3

End

En

Conf t

Router ospf 1

Network 150.1.3.3 0.0.0.0 area 3

Area 3 range 150.1.3.0 255.255.255.0

 

 

Comments

  • Hi cdolores04,

    By default, OSPF will advertise Loopback's with /32 mask, unless we config "ip ospf network-type point-to-point" on the loopback interface. This task does not allow us to do this.

    The other way to advertise the loopback as /24 is using "redistribute connected", but the task requires the interface lo0 of R3 to be associated with an OSPF area.

    The only option here is to use OSPF summarization (Only ABR can do inter area summarization). So, we config Lo0 into an OSPF area. It can be any area as long as R3 is the only ABR for that area. The easiest of course, by creating a new area. SG uses area 3 in this case. And then we configure ABR R3 to summary the /32 route into /24 route.

    Here is the router LSA for Area 3 (taken from R3)
    PS:I am using Rack 8

                    Router Link States (Area 3)

      LS age: 361
      Options: (No TOS-capability, DC)
      LS Type: Router Links
      Link State ID: 150.8.3.3
      Advertising Router: 150.8.3.3
      LS Seq Number: 80000002
      Checksum: 0x9BA6
      Length: 36
      Area Border Router
      Number of Links: 1

        Link connected to: a Stub Network
         (Link ID) Network/subnet number: 150.8.3.3
         (Link Data) Network Mask: 255.255.255.255
          Number of TOS metrics: 0
           TOS 0 Metrics: 1

    But the rest of OSPF routers will see it as 150.8.3.0/24

                OSPF Router with ID (150.8.3.3) (Process ID 1)

                    Summary Net Link States (Area 0)

      LS age: 525
      Options: (No TOS-capability, DC, Upward)
      LS Type: Summary Links(Network)
      Link State ID: 150.8.3.0 (summary Network Number)
      Advertising Router: 150.8.3.3
      LS Seq Number: 80000002
      Checksum: 0xB73D
      Length: 28
      Network Mask: /24
            TOS: 0  Metric: 1


                    Summary Net Link States (Area 34)

      LS age: 525
      Options: (No TOS-capability, DC, Upward)
      LS Type: Summary Links(Network)
      Link State ID: 150.8.3.0 (summary Network Number)
      Advertising Router: 150.8.3.3
      LS Seq Number: 80000002
      Checksum: 0xB73D
      Length: 28
      Network Mask: /24
            TOS: 0  Metric: 1


                    Summary Net Link States (Area 135)

      LS age: 528
      Options: (No TOS-capability, DC, Upward)
      LS Type: Summary Links(Network)
      Link State ID: 150.8.3.0 (summary Network Number)
      Advertising Router: 150.8.3.3
      LS Seq Number: 80000002
      Checksum: 0xB73D
      Length: 28
      Network Mask: /24
            TOS: 0  Metric: 1

  • It will work with area 3 or 34.  Since R3 is terminating the virtual link transiting across area 135, then it is already an ABR.

     

  • It will work with area 3 or 34.

    Hi dunhamdd,

    We cannot use area 34 to meet the task requirement: "This network should appear in all other OSPF enabled routers with a /24 subnet mask"
    If we use area 34, routers in area 34 will see the prefix with /32 subnet mask.
    We should use a new area that only R3 is the member.

  • Hi community,

    Having a issue with ospf loopback host (/32) advertissement, I've a quick look on our community discussion and found that the subject was discussed in the pass.

    So let me try to summarize how to get ospf advertise the  loopback interface network instead of host (/32):

    - configure loopbak interface as point-to-point ospf interface

    - redistribute connected loopback interface

    - summarize the loopack interface with the area range on the ABR  (depending on the scenario a new area can be configured for the Loopback interface).

    Depending on the requirement of the scenario, we can adapt one of these methods.

    Don't hesite to correct/add some idea here.

    Thanks.

  • Hi community,

    Having a issue with ospf loopback host (/32) advertissement, I've a quick look on our community discussion and found that the subject was discussed in the pass.

    So let me try to summarize how to get ospf advertise the  loopback interface network instead of host (/32):

    - configure loopbak interface as point-to-point ospf interface

    - redistribute connected loopback interface

    - summarize the loopack interface with the area range on the ABR  (depending on the scenario a new area can be configured for the Loopback interface).

    Depending on the requirement of the scenario, we can adapt one of these methods.

    Don't hesite to correct/add some idea here.

    Thanks.

    Hi community are you OK with my summary ?

    Thanks

  • Hi Kalmogo,

    Yeah - I like your 3 different answers. Definitely helps to lay down all possible solutions to something before applying requirements. This is good stuff.

    Thanks,

    Mike

  • Good Mike.

    Nice to know that.

    Thanks,

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