OSPF operates within a single autonomous system (AS).
Networks within this single AS, however, can be divided into a number
of areas. By default, Area 0 is created. Area 0 can either function
alone or act as the OSPF backbone for a larger number of areas.
Each OSPF area is named using a 32-bit identifier which in most
cases is written in the same dotted-decimal notation as an IP4 address.
For example, Area 0 is usually written as 0.0.0.0.
The topology of an area is maintained in its own link state database
and is hidden from other areas, which reduces the amount of traffic
routing required by OSPF. The topology is then shared in a summarized
form between areas by a connecting router.