OSPF communication without area 0

[subhojithalder198]

Hi

I am having this setup

R1--R2--R3

R1-R2 are in Area 2 & R2-R3 are in Area3,   Can I communicate in between R1-R3 by any other possible way without adding Area-0

[ghostinthenet]

No. OSPF requires that there be an area 0 for routing between two different areas.

However, because you have a common router (R2) that holds both areas 1 and 3, you can enable inter-area routing easily by creating a loopback interface on R2 and adding it to area 0, meeting OSPF's requirements.

[johnlloyd_13]

Hi,

Yes, you could by using OSPF virtual link or setup GRE tunnels.

See helpful link:

http://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/47866-ospfdb7.html

[ghostinthenet]

Virtual links still require a path back to area 0, which is problematic if there is no area 0. A GRE tunnel will work well if the tunnel itself is in area 0 and there is no common router between the areas, but an area 0 loopback on the common router presents the simplest solution.

[Joseph W. Doherty]

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Posting

Yes, you can.

If, on R2, the two areas are in the same OSPF process, the answer is generally no.  (I write generally, because you could ping or telnet between R1 and R3 across a tunnel [or a new physical interconnection link] but they won't exchange routes.)

However, if you place the areas into different OSPF processes, you can redistribute routes between the OSPF processes on R2.  (Of course, I'm assuming normal OSPF areas.)

[ghostinthenet]

Definitely outside-of-the-box thinking. :)