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In OSPF why we create Area 0 ? If i do not want to create can i start area 1

smcisco
Level 1
Level 1

 

Please tell me if we are using OSPF protocol and i do not want to create area 0? is it possible ? can i start area1 so on.

5 Replies 5

Charles Hill
VIP Alumni
VIP Alumni

Hello,

See link below 

http://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/7039-1.html

Info below came from link above.

 

"Backbone and Area 0

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

The backbone has to be at the center of all other areas, i.e. all areas have to be physically connected to the backbone. The reasoning behind this 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. The following diagram will illustrate the flow of information in an OSPF network:"

 

Hope this helps,

Please rate helpful posts 

Thanks

Hi Junaid,

 

Area 0 is must require for ospf. So it is also known as “Backbone Area”.

As ospf rule, all other areas must have a connection with area 0.

 

Please find attached .docx file.

 

Regards,

Khaleelur Rahman

Thank you

InayathUlla Sharieff
Cisco Employee
Cisco Employee

Junaid,

Most of the people ask this question...and the answer is that "NO" . The OSPF is designed in such a way that it needs to have the area 0 to work followed by other areas. You might have heard or read that if any area wants to talk to other area you need to go through area 0 for this we have some workaround by using virtual links or gre tunnel.

But configuring OSPF without area 0 will not work at all.

 

HTH

Joseph W. Doherty
Hall of Fame
Hall of Fame

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Posting

"It depends".  As the other posters have already noted, OSPF area zero is required to allow multiple OSPF areas to normally intercommunicate (using the same OSPF process).  If you're going to just have a single OSPF area, it doesn't have to be area zero.  Whether to start with area zero, or not, depends on how you anticipate your topology growing.  (When you go to an OSPF multiple area topology, you'll likely need to migrate some routers into a new area number, ideally, you'll want to migrate as few routers as possible.)

One way to have different OSPF areas intercommunicate, without having an area zero, would be to have each OSPF area in its own OSPF process and redistribute between them.  Not something you would normally do unless you have some special needs for route filtering (which can also be done on ABRs, although ASBRs might be a little more flexible).

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