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3-323
Configuring Network Area Addresses
OSPF protocol broadcast messages (i.e., Link State Advertisements or
LSAs) are restricted by area to limit their impact on network performance.
A large network should be split up into separate OSPF areas to increase
network stability, and to reduce protocol traffic by summarizing routing
information into more compact messages. Each router in an area shares
the same view of the network topology, including area links, route
summaries for directly connected areas, and external links to other areas.
Command Usage
• Use the Network Area Address Configuration page to specify an Area
ID and the corresponding network address range. Each area identifies a
logical group of OSPF routers that actively exchange LSAs to ensure that
they share an identical view of the network topology.
• Each area must be connected to a backbone area. This area passes
routing information between other areas in the autonomous system. The
default value 0.0.0.0 is used as the Area ID for the backbone. All routers
must be connected to the backbone, either directly, or through a virtual
link if a direct physical connection is not possible.
• An area initially configured via the Network Area Address Configuration
page is set as a normal area (or transit area) by default. A normal area can
send and receive external Link State Advertisements (LSAs). If
necessary, you can use the Area Configuration page to configure an area
as a stubby area that cannot send or receive external LSAs, or a
not-so-stubby area (NSSA) that can import external route information
into its area (page 3-309).
• An area must be assigned a range of subnetwork addresses. This area and
the corresponding address range forms a routing interface, and can be
configured to aggregate LSAs from all of its subnetwork addresses and
exchange this information with other routers in the network
(page 3-313).