OSPF

[Jaylene]

I'm new in the Networking field. So, maybe my question is dumb, forgive me for that.
My question is - 
Can we use OSPF without backbone area??

[marce1000 · Accepted solution]

 - Check if this thread can provide some insights :

             https://community.cisco.com/t5/other-network-architecture/ospf-linking-two-non-backbone-area-routers/td-p/116002

 M.

[luis_cordova]

Hi @Jaylene 

The quick answer would be no, because it is an OSPF requirement to have an area 0 (backbone).

Check this link:

https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/7039-1.html#t14

Regards

[balaji.bandi]

short answer NO - what is the use case here without OSPF backbone, why do you think you can build one like that?

[Martin L]

only if you have single area you can use OSPF without backbone area; in this case, area x can be any number.

if you have multiple areas, those must go thru backbone area and number must be 0.

Regards, ML
**Please Rate All Helpful Responses **

[Joseph W. Doherty · Accepted solution]

Yes, if as Martin notes, if you only have a single OSPF area. As he, and the other posters have noted, a multi-area, single "AS" OSPF topology requires a backbone area, area zero.

That said, it's also possible to use OSPF without multiple areas without a backbone area zero, provided they are not part of the same OSPF "AS". On Cisco equipment, you can have more than one OSPF process and then you can have traffic flow between the OSPF "ASs".

For the latter, as routes will not "flow" between OSPF processes, by default, you either need to redistribute routes or do something like distribute a default route, from the ASBR into the different OSPF topologies.