Dell SmartFabric OS10 User Guide Release 10.5.3

OSPF operates in a hierarchy. The largest entity within the hierarchy is the autonomous system (AS). The AS is a collection of networks under a common administration that share a common routing strategy. OSPF is an intra-AS, Interior Gateway Routing Protocol (IGRP) that receives routes from and sends routes to other AS.

You can divide an AS into several areas, which are groups of contiguous networks and attached hosts administratively grouped. Routers with multiple interfaces can participate in multiple areas. These routers, called area border routers (ABRs), maintain separate databases for each area. Areas are a logical grouping of OSPF routers that an integer or dotted-decimal number identifies.

Areas allow you to further organize routers within the AS with one or more areas within the AS. Areas allow subnetworks to hide within the AS—minimizing the size of the routing tables on all routers. An area within the AS may not see the details of another area’s topology. An area number or the router’s IP address identifies AS areas.