Cisco Systems 3750E manual Configuring Ospf Area Parameters, 38-31

Chapter 38 Configuring IP Unicast Routing

Configuring OSPF

Configuring OSPF Area Parameters

You can optionally configure several OSPF area parameters. These parameters include authentication for password-based protection against unauthorized access to an area, stub areas, and not-so-stubby-areas (NSSAs). Stub areas are areas into which information on external routes is not sent. Instead, the area border router (ABR) generates a default external route into the stub area for destinations outside the autonomous system (AS). An NSSA does not flood all LSAs from the core into the area, but can import AS external routes within the area by redistribution.

Route summarization is the consolidation of advertised addresses into a single summary route to be advertised by other areas. If network numbers are contiguous, you can use the area range router configuration command to configure the ABR to advertise a summary route that covers all networks in the range.

Note The OSPF area router configuration commands are all optional.

Beginning in privileged EXEC mode, follow these steps to configure area parameters:

	Command	Purpose
Step 1
	configure terminal	Enter global configuration mode.
Step 2
	router ospf process-id	Enable OSPF routing, and enter router configuration mode.
Step 3
	area area-idauthentication	(Optional) Allow password-based protection against unauthorized
		access to the identified area. The identifier can be either a decimal
		value or an IP address.
Step 4
	area area-idauthentication message-digest	(Optional) Enable MD5 authentication on the area.
Step 5
	area area-idstub [no-summary]	(Optional) Define an area as a stub area. The no-summarykeyword
		prevents an ABR from sending summary link advertisements into the
		stub area.
Step 6
	area area-idnssa [no-redistribution]	(Optional) Defines an area as a not-so-stubby-area. Every router
	[default-information-originate]	within the same area must agree that the area is NSSA. Select one of
	[no-summary]	these keywords:
		• no-redistribution—Select when the router is an NSSA ABR and
		you want the redistribute command to import routes into normal
		areas, but not into the NSSA.
		• default-information-originate—Select on an ABR to allow
		importing type 7 LSAs into the NSSA.
		• no-redistribution—Select to not send summary LSAs into the
		NSSA.
Step 7
	area area-id range address mask	(Optional) Specify an address range for which a single route is
		advertised. Use this command only with area border routers.
Step 8
	end	Return to privileged EXEC mode.
Step 9
	show ip ospf [process-id]	Display information about the OSPF routing process in general or for
		a specific process ID to verify configuration.
	show ip ospf [process-id[area-id]]database	Display lists of information related to the OSPF database for a
		specific router.
Step 10
	copy running-config startup-config	(Optional) Save your entries in the configuration file.
		Catalyst 3750-E and 3560-E Switch Software Configuration Guide
OL-9775-02			38-31