OSPF area types
OSPF is built upon a hierarchy of network areas. All areas for a given OSPF domain reside in the same AS. An AS is defined as a number of contiguous networks, all of which share the same interior gateway routing protocol.
An AS can be divided into multiple areas. Each
area represents a collection of contiguous networks and hosts, and
the topology of a given area is not known by the internal routers
in any other area. Areas define the boundaries to which types 1 and
2 LSAs are broadcast, which limits the amount of LSA flooding that
occurs within the AS and also helps to control the size of the LSDBs
maintained in OSPF routers. An area is represented in OSPF by either
an IP address or a number. Area types include:
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All areas in an AS must connect with the backbone through one or more ABRs. If a normal area is not directly connected to the backbone area, it must be configured with a virtual link to an ABR that is directly connected to the backbone. The remaining area types do not allow virtual link connections to the backbone area.
