38-31
Catalyst 3750-E and 3560-E Switch Software Configuration Guide
OL-9775-02
Chapter38 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 ro ute 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
Step1 configure terminal Enter global configuration mode.
Step2 router ospf process-id Enable OSPF routing, and enter router configuration mode.
Step3 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.
Step4 area area-id authentication message-digest (Optional) Enable MD5 authentication on the area.
Step5 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.
Step6 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.
Step7 area area-id range address mask (Optional) Specify an address range fo r which a single route is
advertised. Use this command only with area border routers.
Step8 end Return to privileged EXEC mode.
Step9 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.
Step10 copy running-config startup-config (Optional) Save your entries in the configuration file.