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Community Member

OSPF Area intesection?

How does one determine the start/end of an area?

For instance:

NetA -- RtrA ----- RtrB -- NetB

In the above example, RtrA and RtrB both have 2 interfaces.

If RtrA and NetA comprise area 0, and RtrB and NetB comprise Area 1

where do Area 0 and 1 meet?

Is the interface linking Area 0 to 1 in area 0 or area 1 on RtrA and RtrB?


Community Member

Re: OSPF Area intesection?

You define this by yourself through the configuration of your OSPF routing protocol. The subnet X between RtrA and RtrB in your example will reside into area 0 if you configure "network X area 0" on both routers and will be in area 1 if you configure "network X area 1" on both routers. In the first case RtrB will be the ABR; in the second case RtrA will perform this task.




Re: OSPF Area intesection?

Thanks for your reply, but how is this then extended to the following concept?

NetC -- RtrC ---- RtrB ---- RtrA -- NetA

Again RtrA is in area 0, Rtr B in Area 1, and RtrC in area 2.

From the OSPF Design guide, I think I need a Virtual link transit through area 1, but if I extend Area 0 to the interface on RtrB, I don't need the virtual link any more? In this case Area 1 would also be extended to the link interface on RtrC?

Community Member

Re: OSPF Area intesection?

this option would eliminate the need for the virtual link throught area 1, but you cannot assign an interface to 2 areas. Hence, if you extend area 0 to RTR B, you would not be able to use Area 1 anymore. Area2 would connect directly to area 0 on router RtrB.

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