The OSPF ABR Type 3 LSA Filtering feature extends the ability of an ABR that is running the OSPF protocol to filter type 3 link-state advertisements (LSAs) that are sent between different OSPF areas. This feature allows only packets with specified prefixes to be sent from one area to another area and restricts all packets with other prefixes. This type of area filtering can be applied out of a specific OSPF area, into a specific OSPF area, or into and out of the same OSPF areas at the same time.
History for the OSPF ABR Type 3 LSA Filtering Feature
This feature was introduced.
This feature was integrated into Cisco IOS Release 12.2(4)T.
Support for the Cisco 7500 series was added in Cisco IOS Release 12.2(4)T3.
Support for the Cisco 1710, 1721, 3631, 3725, 3745 and IGX 8400 series URM was added in Cisco IOS Release 12.2(8)T.
Support for the Cisco AS5300, AS5400, and AS5800 series was integrated into Cisco IOS Release 12.2(11)T.
This feature was integrated into Cisco IOS Release 12.2(28)SB.
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The OSPF ABR Type 3 LSA Filtering feature gives the administrator improved control of route distribution between OSPF areas.
Only type 3 LSAs that originate from an ABR are filtered.
This feature is an extension of the OSPF routing protocol. For more information about configuring OSPF and configuring route summarization and filtering, refer to the "OSPF" module of the Cisco IOS IP Configuration Guide, Release 12.4 and the Cisco IOS IP Routing Protocols Command Reference, Release 12.4T.
See the following sections for configuration tasks for the OSPF ABR Type 3 LSA Filtering feature. Each task in the list is identified as either required or optional:
Creates a prefix list with the name specified for the list-name argument.
Verifying OSPF ABR Type 3 LSA Filtering
To verify that the OSPF ABR Type 3 LSA Filtering feature has been configured, use the showipospf command in the EXEC mode. The showipospf 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 showipospf command:
router# show ip ospf 1 Routing Process "ospf 1" with ID 172.16.0.1 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 10.0.0.0/8 Passive Advertise Area-filter AREA_0_IN in Area-filter AREA_0_OUT out Number of LSA 5. Checksum Sum 0x29450 Number of opaque link LSA 0. Checksum Sum 0x0 Number of DCbitless LSA 0 Number of indication LSA 0 Number of DoNotAge LSA 0 Flood list length 0 Area 1 Number of interfaces in this area is 1 Area has no authentication SPF algorithm executed 4 times Area ranges are Area-filter AREA_1_IN in Area-filter AREA_1_OUT out Number of LSA 6. Checksum Sum 0x30100 Number of opaque link LSA 0. Checksum Sum 0x0 Number of DCbitless LSA 0 Number of indication LSA 0 Number of DoNotAge LSA 0 Flood list length 0
Monitoring and Maintaining OSPF ABR Type 3 LSA Filtering
Displays information about a prefix list or prefix list entries.
The following configuration example output shows interarea filtering that is applied to both incoming and outgoing routes:
Router(config)# router ospf 1 log-adjacency-changes area 1 filter-list prefix AREA_1_OUT outarea 3 filter-list prefix AREA_3_IN in network 10.0.0.0 0.255.255.255 area 3 network 172.16.1.0 0.0.0.255 area 0 network 192.168.0.0 0.255.255.255 area 1!ip prefix-list AREA_1_OUT seq 10 permit 10.25.0.0/8 ge 16ip prefix-list AREA_1_OUT seq 20 permit 172.20.20.0/24!ip prefix-list AREA_3_IN seq 10 permit 172.31.0.0/16!
The following sections provide references related to OSPF ABR Type 3 LSA Filtering.
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