Ethernet Switching
Ethernet Switching

OSPF Virtual Links

‎04-28-2020 03:56 PM

HI Team , i have a some questiones regarding the ospf virtual links. Topology is as below.


  1. how can i communicate between Area0 and Area 3. do i need to create virutal link from ( B to C and C to D) or (B to C and B to D) ?

  2. How many transit area's can be used in Virtual link ?

  3. what type of LSA exchanged over Virtual link ?ospf area.jpgThanks in Advance

Ethernet Switching

Re: OSPF Virtual Links

‎04-28-2020 09:06 PM

Hi Sunil,


Virtual links are used to communicate an area with the backbone (area 0) through another area that has already a physical connection to the backbone. As you know, OSPF areas must be adjacent to area 0 to work.


In your scenario, Area 1 would be a transit area containing a virtual link for Area 2 to reach Area 0. 


Here is what I have found on it: 

"To configure an OSPF virtual link through an area, you specify the router ID (IP address) of the routing devices at each end of the virtual link. These routing devices must be area border routers (ABRs), with one that is physically connected to the backbone. "


Therefore, since Area 1 is the only one that is physically connected to the backbone, it would be the only area that can be used as a transit area for a virtual link. Area 3 would not be possible and a 0/0 route pointing to area 2 can be used instead.


I would expect to see LSA type 3 and type 4 for any ASBR on the network, since the Area 2 in this case will have the same routing database on OSPF as the rest of the domain.