Downloads |
Table Of Contents
Related Features and Technologies
Supported Standards, MIBs, and RFCs
Configuring OSPF ABR Type 3 LSA Filtering
Verifying OSPF ABR Type 3 LSA Filtering
Monitoring and Maintaining OSPF ABR Type 3 LSA Filtering
OSPF ABR Type 3 LSA Filtering
Feature History
This feature module describes filtering interarea routes on an Area Border Router (ABR) with the Open Shortest Path First (OSPF) protocol. It includes the following sections:
•
Related Features and Technologies
•
Feature Overview
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. This feature is supported by the addition of the area filter-list command in router configuration mode.
Benefits
The OSPF ABR Type 3 LSA Filtering feature gives the administrator improved control of route distribution between OSPF areas.
Restrictions
Only type 3 LSAs that originate from an ABR are filtered.
Related Features and Technologies
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" chapter of the Release 12.2 Cisco IOS IP Configuration Guide and the Cisco IOS IP Command Reference, Volume 2 of 3: Routing Protocols.
Supported Platforms
The OSPF ABR Type 3 LSA Filtering feature is supported for the following platforms in Cisco IOS Release 12.2(11)T:
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Determining Platform Support Through Cisco Feature Navigator
Cisco IOS software is packaged in feature sets that are supported by specific platforms. To get updated information regarding platform support for this feature, access Cisco Feature Navigator. Cisco Feature Navigator dynamically updates the list of supported platforms as new platform support is added for the feature.
Cisco Feature Navigator is a web-based tool that enables you to determine which Cisco IOS software images support a specific set of features and which features are supported in a specific Cisco IOS image. You can search by feature or release. Under the release section, you can compare releases side by side to display both the features unique to each software release and the features in common.
To access Cisco Feature Navigator, you must have an account on Cisco.com. If you have forgotten or lost your account information, send a blank e-mail to cco-locksmith@cisco.com. An automatic check will verify that your e-mail address is registered with Cisco.com. If the check is successful, account details with a new random password will be e-mailed to you. Qualified users can establish an account on Cisco.com by following the directions at http://www.cisco.com/register
Cisco Feature Navigator is updated regularly when major Cisco IOS software releases and technology releases occur. For the most current information, go to the Cisco Feature Navigator home page at the following URL:
Availability of Cisco IOS Software Images
Platform support for particular Cisco IOS software releases is dependent on the availability of the software images for those platforms. Software images for some platforms may be deferred, delayed, or changed without prior notice. For updated information about platform support and availability of software images for each Cisco IOS software release, refer to the online release notes or, if supported, Cisco Feature Navigator.
Supported Standards, MIBs, and RFCs
Standards
No new or modified standards are supported by this feature.
MIBs
No new or modified MIBs are supported by this feature.
To obtain lists of supported MIBs by platform and Cisco IOS release, and to download MIB modules, go to the Cisco MIB website on Cisco.com at the following URL:
http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml
RFCs
No new or modified standards are supported by this feature.
Configuration Tasks
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:
•
•
Configuring OSPF 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 OSPF 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 1Routing Process "ospf 1" with ID 172.16.0.1Supports only single TOS(TOS0) routesSupports opaque LSAIt is an area border routerSPF schedule delay 5 secs, Hold time between two SPFs 10 secsMinimum LSA interval 5 secs. Minimum LSA arrival 1 secsNumber of external LSA 0. Checksum Sum 0x0Number of opaque AS LSA 0. Checksum Sum 0x0Number of DCbitless external and opaque AS LSA 0Number of DoNotAge external and opaque AS LSA 0Number of areas in this router is 2. 2 normal 0 stub 0 nssaExternal flood list length 0Area BACKBONE(0)Number of interfaces in this area is 2Area has no authenticationSPF algorithm executed 6 timesArea ranges are10.0.0.0/8 Passive AdvertiseArea-filter AREA_0_IN inArea-filter AREA_0_OUT outNumber of LSA 5. Checksum Sum 0x29450Number of opaque link LSA 0. Checksum Sum 0x0Number of DCbitless LSA 0Number of indication LSA 0Number of DoNotAge LSA 0Flood list length 0Area 1Number of interfaces in this area is 1Area has no authenticationSPF algorithm executed 4 timesArea ranges areArea-filter AREA_1_IN inArea-filter AREA_1_OUT outNumber of LSA 6. Checksum Sum 0x30100Number of opaque link LSA 0. Checksum Sum 0x0Number of DCbitless LSA 0Number of indication LSA 0Number of DoNotAge LSA 0Flood list length 0Monitoring and Maintaining OSPF ABR Type 3 LSA Filtering
Router# show ip prefix-list
Displays information about a prefix list or prefix list entries.
Configuration Examples
The following configuration example output shows interarea filtering that is applied to both incoming and outgoing routes:
Router(config)# router ospf 1log-adjacency-changesarea 1 filter-list prefix AREA_1_OUT outarea 3 filter-list prefix AREA_3_IN innetwork 10.0.0.0 0.255.255.255 area 3network 172.16.1.0 0.0.0.255 area 0network 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!Command Reference
This section documents the new area filter-list command that configures the OSPF ABR Type 3 LSA Filtering feature. All other commands used with this feature are documented in the Cisco IOS Release 12.2 command reference publications.
area filter-list
To filter prefixes advertised in type 3 link-state advertisements (LSAs) between Open Shortest Path First (OSPF) areas of an Area Border Router (ABR), use the area filter-list command in router configuration mode. To change or cancel the filter, use the no form of this command.
area {area-id} filter-list prefix {prefix-list-name in | out}
no area {area-id} filter-list prefix {prefix-list-name in | out}
Syntax Description
Defaults
This command has no default behavior.
Command Modes
Router configuration
Command History
12.0(15)S
This command was introduced.
12.2(4)T
This command was integrated into Cisco IOS Release 12.2(4)T.
Usage Guidelines
With this feature enabled in the "in" direction, all type 3 LSAs originated by the ABR to this area, based on information from all other areas, are filtered by the prefix list. Type 3 LSAs that were originated as a result of the area range command in another area are treated like any other type 3 LSA that was originated individually. Any prefix that does not match an entry in the prefix list is implicitly denied.
With this feature enabled in the "out" direction, all type 3 LSAs advertised by the ABR, based on information from this area to all other areas, are filtered by the prefix list. If the area range command has been configured for this area, type 3 LSAs that correspond to the area range are sent to all other areas, only if at least one prefix in the area range matches an entry in the prefix list.
If all specific prefixes are denied by the prefix list, type 3 LSAs that correspond to the area range command will not be sent to any other area. Prefixes that are not permitted by the prefix list are implicitly denied.
Examples
The following example filters prefixes that are sent from all other areas to area 1:
area 1 filter-list prefix AREA_1 inRelated Commands