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Forum Replies

  1. Hi John,

    Good question, the only other option where you can set the DNA bit is the “on demand circuit”. This can be used for (WAN) links where you pay for a certain amount of bytes of per minute/second. You don’t want to refresh LSAs on these links since they will keep the link up.

    I guess that’s why they also decided to set the DNA bit for the virtual link in case you have links like this.


  2. Hello Stuart.

    Here is the diagram that Rene has in his lesson:


    A virtual link has been created between the L0 interface of R1 and the Fa1/0 interface of R2.

    The OSPF packets between the two ends of the virtual link are not multicast packets. (Note the two ends of the virtual link are the L0 interface of R1 and the Fa1/0 interface of R2). LSAs that are sent over the virtual link are actually tunnelled packets between and, based on the ne

    ... Continue reading in our forum

  3. Hi Laz,
    I think you can’t catch my question…
    Visualize a topology like …

    area0>> Area-1 stub/nssa >> Area-2
    so upon on above scenario the Area-2 have to connect to Area-0 using Virtual link to make the area functioning. Technically Virtual link not possible over the Stub/nssa area why ?? Thx


  4. Hi Zeko,

    If you enable authentication for virtual links, you have to enable it globally for area 0 and set the password on the virtual link command. Here’s an example:

    R1#show run | begin ospf
    router ospf 1
     area 0 authentication
     area 1 virtual-link authentication-key NWL

    Authentication is enabled for area 0, the virtual link goes through area 1 and has the password. You can see it works with this command:

    R1#show ip ospf virtual-links 
    Virtual Link OSPF_VL0 to router is up
      Run as demand circuit
      DoNotAge LSA allowed.
      Transit area 1,
    ... Continue reading in our forum

  5. Hello Sovandara,

    You can create more than one virtual link if needed. For example, let’s say you have a topology like this:

    (area 0) R1 (area 1) R2 (area 2) R3 (area 3)

    You can configure a virtual link between R1-R2 to get area 2 connected to area 0. The virtual link is like a tunnel that gives R2 access to area 0.

    You can then configure a virtual link between R2 and R3 to connect area 3 to area 0.

    Hope this helps!


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