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Cisco ME 3800X and 3600X Switch Software Configuration Guide
OL-23400-01
Chapter 29 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-id authentication
(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-id authentication message-digest (Optional) Enable MD5 authentication on the area.
Step 5
area area-id stub [no-summary]
(Optional) Define an area as a stub area. The no-summary keyword
prevents an ABR from sending summary link advertisements into the
stub area.
Step 6
area area-id nssa [no-redistribution]
[default-information-originate]
[no-summary]
(Optional) Defines an area as a not-so-stubby-area. Every router
within the same area must agree that the area is NSSA. Select one of
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]
show ip ospf [process-id [area-id]] database
Display information about the OSPF routing process in general or for
a specific process ID to verify configuration.
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.
