Editing Open Shortest Path First (section)

===Backbone area===
[[File:OSPF-area0 standalone figur.drawio.png|frameless|right|Example of backbone, area 0 with 2 routers, R1 and R2]]
The backbone area (also known as ''area 0'' or ''area 0.0.0.0'') forms the core of an OSPF network. All other areas are connected to it, either directly or through other routers. OSPF requires this to prevent [[routing loop]]s.<ref>{{cite web |last1=Doyle |first1=Jeff |title=My Favorite Interview Question |url=https://www.networkworld.com/article/2348778/my-favorite-interview-question.html |website=Network World |access-date=28 December 2021 |language=en |date=10 September 2007 |archive-date=December 28, 2021 |archive-url=https://web.archive.org/web/20211228182634/https://www.networkworld.com/article/2348778/my-favorite-interview-question.html |url-status=live }}</ref> Inter-area routing happens via routers connected to the backbone area and to their own associated areas. It is the logical and physical structure for the 'OSPF domain' and is attached to all nonzero areas in the OSPF domain. In OSPF the term ''autonomous system boundary router'' (ASBR) is historic, in the sense that many OSPF domains can coexist in the same Internet-visible autonomous system, RFC 1996.<ref>{{Harv|ASGuidelines|1996|p=25}}</ref>{{Ref RFC|1930}}

All OSPF areas must connect to the backbone area. This connection, however, can be through a virtual link. For example, assume area 0.0.0.1 has a physical connection to area 0.0.0.0. Further assume that area 0.0.0.2 has no direct connection to the backbone, but this area does have a connection to area 0.0.0.1. Area 0.0.0.2 can use a virtual link through the ''transit area'' 0.0.0.1 to reach the backbone. To be a transit area, an area has to have the transit attribute, so it cannot be stubby in any way.