Cisco Cisco IOS Software Release 12.0(15)S White Paper

ABR Type 3 LSA Filtering

Configuration Tasks

Cisco IOS Release 12.0(15)S

Configuring ABR Type 3 LSA Filtering

To filter interarea routes into a specified area, use the following commands beginning in router
configuration mode:

To filter interarea routes out of a specified area, use the following commands beginning in router
configuration mode:

Verifying ABR Type 3 LSA Filtering

To verify that the OSPF ABR Type 3 LSA Filtering feature has been configured, use the show ip ospf
EXEC command. The show ip ospf command will show that this feature has been enabled by listing
the area filter as “in” or “out.” The following is sample output from the show ip ospf command:

router# show ip ospf 1

Routing Process "ospf 1" with ID 177.0.0.1

Supports only single TOS(TOS0) routes

Supports opaque LSA

It is an area border router

SPF schedule delay 5 secs, Hold time between two SPFs 10 secs

Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs

Number of external LSA 0. Checksum Sum 0x0

Number of opaque AS LSA 0. Checksum Sum 0x0

Number of DCbitless external and opaque AS LSA 0

Number of DoNotAge external and opaque AS LSA 0

Number of areas in this router is 2. 2 normal 0 stub 0 nssa

External flood list length 0

Area BACKBONE(0)

Number of interfaces in this area is 2

Area has no authentication

SPF algorithm executed 6 times

Area ranges are

39.0.0.0/8 Passive Advertise

Command

Purpose

Step 1

Router(config)# router ospf process-id

Configures the router to run an OSPF process.

Step 2

Router(config-router)# area area-id filter-list prefix

prefix-list-name in

Configures the router to filter interarea routes into
the specified area.

Step 3

Router(config-router)# ip prefix-list list-name [seq

seq-value] deny | permit network/len [ge ge-value] [le

le-value]

Creates a prefix list with the name specified for the
list-name argument.