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Community Member

Two diffrent OSPF areas across the same physical connection?

I am working on a disaster recovery design and have worked my self into a corner. I need for two routers with a Ethernet connection between them. Across this segment I need to have the two routers establish adjacency with two diffrent non 0 areas.

router a ----- area 1 & area 9 ----- router b

Can this be done? I have attempted using one logical connection (no vlans) and with two logical connections (two vlans). Each only provided adjacency in one area not both.

Would putting a switch between the two routers have any impact?

Thanks!

4 REPLIES
Community Member

Re: Two diffrent OSPF areas across the same physical connection?

I believe they will not form adjacency unless until we use atleast one common area in both the routers.

Gold

Re: Two diffrent OSPF areas across the same physical connection?

You can't build an adjacency between routers in two different areas. You can configure both of them in the same area on this ethernet link, and get them to form an adjacency, but they won't flood LSA's across the border, or forward traffic across the link. Once you've built this adjacency, though, you can build a virtual link back to area 0, allowing traffic to use this path as a backup, if you want.

So, you could do this:

(area 1)-router a-(area 9)--e/net--(area 9)-router b- (area 9)

Then configure a virtual link from area 1 on router a, though area 9, into area 0. Woudl this do what you want?

Russ.W

Community Member

Re: Two diffrent OSPF areas across the same physical connection?

Both routers have the same two areas.

Router A

Fast 0/0.1 area 1

Fast 0/0.2 area 9

Router B

Fast 0/0.1 area 1

Fast 0/0.2 area 9

There is only one ospf process on each router

Gold

Re: Two diffrent OSPF areas across the same physical connection?

Which interfaces connect to which routers? Are f0/0.2 connected directly between the two routers? If so, then they should form an adjacency, you just won't route across the interfaces, since no type 3's will be built into the area.

Russ.W

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