Specifications

Chapter 2. IBM System Networking Switch 10Gb Ethernet switch features 63
OSPF defines the following types of areas (shown in Figure 2-8):
򐂰 Stub area: An area that is connected to only one other area. External route information is
not distributed into stub areas.
򐂰 Not-So-Stubby-Area (NSSA): Similar to a stub area with additional capabilities. Routes
originating from within the NSSA can be propagated to adjacent transit and backbone
areas. External routes from outside the AS can be advertised within the NSSA but are not
distributed into other areas.
򐂰 Transit Area: An area that allows area summary information to be exchanged between
routing devices. The backbone (area 0), any area that contains a virtual link to connect
two areas, and any area that is not a stub area or an NSSA are considered transit areas.
Figure 2-8 OSPF area types