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Why does OSPF need backbone area?



Why does OSPF require all traffic between non-backbone areas to pass through a backbone area (area 0)?
 
Because inter-area OSPF is distance vector, it is vulnerable to routing loops. It avoids loops by mandating a loop-free inter-area topology, in which traffic from one area can only reach another area through area 0.

Ref : Jeff Doyle article at Network world

http://www.networkworld.com/article/2348778/cisco-subnet/my-favorite-interview-question.html
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