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Why OSPF area 0 is backbone & how to change backbone?

Why OSPF area 0 is backbone & how to change backbone area ?

6 REPLIES

Why OSPF area 0 is backbone & how to change backbone?

Mahadev,

To understand why OSPF needs OSPF Area 0, you need to understand the different between Distance Vector and Link State Routing protocols.

With Distance Vector routing protocols, each router relies on its "neighbor" to tell it about the other parts of the network. IT has to "trust" that it's neighbor is telling it the truth so to speak, about all networks it knows about.

With Link State routing protocols, network information, is distributed in the form of Link State Advertisements (LSAs) and each router knows about the entire network from it's own local point of view.

So When you have a single area, for example, area 100, all the routers within it's area, knows about all the other networks, and routers via Link State Advertisements (LSA Type 1 and 2) to be exact depending on what you have going on.

But if you want to connect multiple OSPF Area's, the routers that connect these areas are called ABRs or Area Border Routers. So if you want to connect OSPF Area 200 to 100, the ABR  inbetween Area 100 and 200, will be Distance Vector between the different areas not Link State. This could cause a routing loop, because OSPF Area 100, is "trusting" that the ABR is telling it the truth. Routers in OSPF Area 100 do not have any sort of topology information about anything going on in OSPF Area 200.

So OSPF came up with OSPF Area 0, which is basically a middle man so to speak. So networks from OSPF Area 100, will be advertised in LSAs (Link State Advertisements) to the ABR, which will insert them into OSPF Area 0, and then OSPF Area 0, will distribute them into OSPF Area 200. This allows for a loop free network.

And you can't change the OSPF Backbone Area 0.

I hope this helps.

New Member

Why OSPF area 0 is backbone & how to change backbone?

John,

1. In interview it is been ask how to change Backbone area 0 ?

2. Let me know the Rules of Backbone area 0 & Non-backbone area ?

Why OSPF area 0 is backbone & how to change backbone?

from the perspective in the RFC written by Jhon T Moy, the Area 0 is the backbone... so it's not be able to change it !

It's by design the Area 0 the Backbone.

had a great day . best regards, and rate if you'll find this post useful
New Member

Why OSPF area 0 is backbone & how to change backbone?

Thanks,

But i have ask to only 2 qution.

1. In interview it is been ask how to change Backbone area 0 ?

2. Let me know the Rules of Backbone area 0 & Non-backbone area ?

Why OSPF area 0 is backbone & how to change backbone?

Those info you could find on Jeff Doyle TCP/IP Routing Vol 1... and on his other book OSPF and IS-IS ....

good reading .....

had a great day . best regards, and rate if you'll find this post useful
New Member

Why OSPF area 0 is backbone & how to change backbone?

Thanks

But I have not find out my ans in this Books.

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