OSPF, Area 0

[jdsalminen]

As I understand it OSPF area 0 and other OSPF areas must have a 'connection' to area 0 in order to construct a consistent ospf database.

My question is what technically is a 'connection'?

I know that a router that has an interface in area 0 is a connection. But what about a router that does not have an interface in area 0? Does a neighbor relationship to an area 0 router suffice?

[amit-singh]

No, If a router is in another area, it will not form a neighbor relationship with the router in another area.

Here are some points in which routers will not become neighbor.

1 If Hello/Dead interval are diff.

2 If routers are in diff area.

3 If routers interface network subnet mask is different.

4 If a router is in stub area and the neighbor is not.

5 If authentication is configured and doesnot match.

HTH, please rate if it does.

-amit singh

[balajitvk]

Hi,

All areas in an Open Shortest Path First (OSPF) autonomous system must be physically connected to the backbone area (Area 0).

In addtion to amit, where this is not possible, you can use a virtual link to connect to the backbone through a non-backbone area. You can also use virtual links to connect two parts of a partitioned backbone through a non-backbone area

Or even u can have GRE tunnel insted of this creating virtual link between those two routers.

There is a link to explain this in detail,

http://www.cisco.com/en/US/tech/tk365/technologies_configuration_example09186a00801ec9ee.shtml#using

Rate if it helps,

-balaji.

[jdsalminen]

If you have a group of routers that are only in area 10 and one router that is in area 0 and area 10 and every router can establish a neighbor relationship with the ABR router.

Does that suffice as a 'connection' to area 0 for the routers in area 10?

[Richard Burts]

Joel

Yes that would certainly suffice as a connection to area 0. In fact it is not necessary that all routers form a neighbor relationship with the ABP directly. It is sufficient that within the interconnected routers of the area that at least one has a connection to area 0.

HTH

Rick