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Forum Replies

  1. Another bit of information: OSPF VLs cannot be constructed if the interface from which the VL would recurse, on either end, is unnumbered. In the first example the Nancy Fa0/0 and Donna Fa0/0 would have to have real IP addresses on them. However, OSPF VLs can transit unnumbered interfaces if those links are in the middle of the area. If area 1 were much larger, and some of the intermediary links were unnumbered, that would work fine. Reason is because although OSPF VLs behave like demand circuits, initially they send unicast hellos between exit interfaces and this must have a real IP address.

  2. Hi Rene,

    I configured Discontiguous area 0 for virtual links,by default if we enable loopback interface on the router,it takes loop back interface., i.e as the router ID and one more thing with lab,i get error message like mismatch in the area ID,before I configure a virtual link between router Nancy and Susan.

    This lab dint work the way its show in the figure.Need your help in this rene.

  3. 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 t

    ... Continue reading in our forum

  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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