OSPF single area design

Unanswered Question
May 7th, 2008

If a network has to be designed with just a single OSPF area, which area will be used.

i suppose any area id can be used since the traffic would be limited to a single area & doesnt have to transit across different area id's in which case area 0 may have been used.

Just wanted to know if the concepts are right.

I have this problem too.
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guruprasadr Wed, 05/07/2008 - 07:03

HI BVS, [Pls Rate if HELPS]

In addition to Kevin's POST.

OSPF has special restrictions when multiple areas are involved. If more than one area is configured, one of these areas has to be Area 0. This is called backbone. When designing networks it is good practise to start with Area 0 and then expand into other areas later on.

The Backbone has to be center for all other areas ie., all areas have to be physically connected to Backbone. The reason behind that is that OSPF expects all areas to inject routing information into the backbone and in turn the backbone will disseminate that information into other areas.

To just startup & run with only as "Single Area OSPF", any Area can be defined with any process id.

Hope I am Informative.


Best Regards,

Guru Prasad R

bvsnarayana03 Wed, 05/07/2008 - 10:20

Points to u.

Dude, consider a scenario where four of my interfaces on a router are each in separate area. But they all talk to each other without any backbone configured. If a backbone (area0)is req for inter-area communication, how does the above communication take place.

ruwhite Wed, 05/07/2008 - 12:33

There are two ways this could work:

1. There is a default route being advertised into all the areas from the one router connected to all of them. This would draw all the interarea traffic to the one router in the network with full routing knowledge.

2. http://www.ietf.org/rfc/rfc3509.txt

Other than one of these two being true, it shouldn't work.



tj.mitchell Wed, 05/07/2008 - 18:30

This works because if you take OSPF off, you should still get between interfaces. They are connected interfaces in the routing table, not OSPF routes.

Your going to be able to route between interfaces because that's what a router does.


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