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New Member

IP unnumbered and Virtual link

Hi All,

Can I use IP unnumbered as an OSPF Virtual link? In my lab, when I changed the interface to IP unnumbered, the virtual link would be down. Please explain it.

Thanks advance.


New Member

Re: IP unnumbered and Virtual link

Hi Banlan,

This is not possible. The reason being that the transit area that the virtual link traverses must have full routing information which requires the virtual link to be numbered.

Using numbered interfaces ,If you do a debug ip ospf adj with adjacencies that use a virtual link ,when the adjacency is created you can see that the RIDs are exchanged along with the Virtual link (VL) and the virtual links IP address.

With IP unnumbered the adjacencies will not establish and the link will not come up.

Unless I am mistaken ........

New Member

Re: IP unnumbered and Virtual link


I am indeed mistaken......You can have unnumbered virtual links.

Virtual links are treated as unaddressed interfaces belonging to the backbone. In order to get this to work you need to have a route between the two ABRs that make the link. When this route is installed in the routing table the interfaces will come up and the adjacency establishes.

Source : page 466 of TCP/IP vol 1 by Doyle

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