Table of Contents

Syntax Description
Usage Guidelines
Keywords
Examples
Related Commands

OSPF Area

This section defines configuration parameters for an OSPF area.

Syntax Description

Number	The area number as an integer.
IP_address	The IP address of the interface for which you are configuring the area.

Usage Guidelines

An area is a generalization of an IP subnetted network within an Autonomous System (AS). An AS is a collection of networks under a common administration sharing a common routing strategy. All routers within an area have the same link-state database. An interface can only belong to one area, although different interfaces on a router can belong to different areas, making the router an Area Border Router. Area Border Routers disseminate routing information or routing changes between areas.

If more than one area is configured within an AS, then one of these areas has to be area 0, which is the backbone. The backbone has to be physically connected to all other areas. The only exception is for virtual links, which are explained in the OSPF Virtual Link section. When designing networks it is good practice to start with area 0 and then expand into other areas later on.

Keywords

After entering the configure command for the section, enter one or more of the following keywords.

OSPFAuthtype = {None | Simple}	The OSPFAuthtype keyword specifies whether the router will perform authentication of Link State Advertisements received from other routers. If Simple is specified, then you need to specify an authentication password using the Authkey keyword in the IP section for any interface which is associated with this area. If None is specified, no authentication will be done on Link State Advertisements. None is the default.
StubArea = {On | Off}	The StubArea keyword sets whether this area will function as a stub area. A stub area is an area which cannot receive external advertisements, which means RIP or static routes will not be redistributed into this area. If routing from a stub area to external routes (i.e., non-OSPF routes) is needed, a default route must be set. A stub area may not be a transit area for a virtual link. Note   The backbone area (area 0) cannot be designated as a stub area.
StubDefaultCost = Number	The StubDefaultCost keyword sets the cost of the default route which will be used by routers within the stub area to route to external destinations. The value can be a number between 0 and 65,535.
NetRange = {Off | On IP_Address IP_Subnet_Mask [Advertise | DoNotAdvertise]}	The NetRange keyword can be used to consolidate routing information at area boundaries, or to hide routing information from routers outside the area. Net ranges only apply to inter-area networks; if all the routers are in one area, any defined net ranges will not be used by the router. This keyword may appear multiple times within the configuration in order to specify several different ranges. On | Off   On specifies that a Net Range is being used. Off indicates that a Net Range is not being used. IP_Address   This is the IP address of the Net Range. IP_Subnet_Mask   This is the subnet mask of the Net Range. Advertise | DoNotAdvertise   This is an optional parameter. If Advertise is specified, the net range will be advertised to other areas. If DoNotAdvertise is specified, the network in the net range will not be advertised to other areas. Note   DoNotAdvertise only applies to OSPF routes and not to routes learned from external protocols using IP route redistribution. External routes must be excluded by using route filtering. See the IP Route Redistribution section.

Examples

This example shows a Net Range being used to consolidate information for subnets 198.41.9.32, 198.41.9.64, 198.41.9.96 and 198.41.9.128, all of which have a subnet mask of 255.255.255.224.

OSPFAuthtype     = "None"    
StubArea         = Off       
NetRange         = On 198.41.9.0 255.255.255.0 Advertise

Related Commands

Command	Description
configure IP	Configures IP parameters for an interface
configure IP Protocol Precedence	Configures the precedence order for routes in the routing table
configure OSPF Virtual Link	Configures OSPF to allow an area that is not contiguous to the backbone area (area 0) to operate
edit config IP Route Filter	Creates IP route filters
show ospf	Shows OSPF configuration and statistics

Posted: Wed Sep 27 10:45:20 PDT 2000
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