Cisco IOS IP Routing Protocols Configuration Guide, Release 12.2SR
OSPF Update Packet-Pacing Configurable Timers
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Table Of Contents

OSPF Update Packet-Pacing Configurable Timers

Feature Overview

Benefits

Restrictions

Related Features and Technologies

Supported Platforms

Supported Standards, MIBs, and RFCs

Configuration Tasks

Configuring OSPF Packet-Pacing Timers

Verifying OSPF Packet-Pacing Timers

Troubleshooting Tips

Monitoring and Maintaining OSPF Packet-Pacing Timers

Configuration Examples

Flood Pacing Example

Retransmission Pacing Example

Group Pacing Example

Command Reference


OSPF Update Packet-Pacing Configurable Timers

Feature History

Release
Modification

12.2(4)T

This feature was introduced.

12.2(4)T3

Support for the Cisco 7500 series was added in Cisco IOS Release 12.2(4)T3.

12.2(8)T

Support for the Cisco 1710, 3631, 3725, 3745, and URM was added in Cisco IOS Release 12.2(8)T.

12.2(8)T1

Support for the Cisco 2691 was added in Cisco IOS Release 12.2(8)T1.

12.2(14)S

This feature was integrated into Cisco IOS Release 12.2(14)S.


This feature module describes the OSPF Update Packet-Pacing Configurable Timers feature. It includes the following sections:

•Feature Overview

•Benefits

•Related Features and Technologies

•Supported Platforms

•Supported Standards, MIBs, and RFCs

•Configuration Tasks

•Monitoring and Maintaining OSPF Packet-Pacing Timers

•Configuration Examples

•Command Reference

Feature Overview

In rare situations, you might need to change Open Shortest Path First (OSPF) packet-pacing default timers to mitigate CPU or buffer utilization issues associated with flooding very large numbers of link-state advertisements (LSAs). The OSPF Update Packet-Pacing Configurable Timers feature allows you to configure the rate at which OSPF LSA flood pacing, retransmission pacing, and group pacing updates occur.

Configuring OSPF flood pacing timers allows you to control interpacket spacing between consecutive link-state update packets in the OSPF transmission queue. Configuring OSPF retransmission pacing timers allows you to control interpacket spacing between consecutive link-state update packets in the OSPF retransmission queue. Cisco IOS software groups the periodic refresh of LSAs to improve the LSA packing density for the refreshes in large topologies. The group timer controls the interval used for group LSA refreshment; however, this timer does not change the frequency that individual LSAs are refreshed (the default refresh occurs every 30 minutes).

Note The default settings for OSPF packet pacing timers are suitable for the majority of OSPF deployments. You should change the default timers only as a last resort.

Benefits

The OSPF Update Packet-Pacing Configurable Timers feature provides the administrator with a mechanism to control the rate at which LSA updates occur in order to reduce high CPU or buffer utilization that can occur when an area is flooded with a very large number of LSAs.

Restrictions

Do not change the packet pacing timers unless all other options to meet OSPF packet flooding requirements have been exhausted. Specifically, network operators should prefer summarization, stub area usage, queue tuning, and buffer tuning before changing the default timers. Furthermore, there are no guidelines for changing timer values; each OSPF deployment is unique and should be considered on a case-by-case basis. The network operator assumes risks associated with changing the default timer values.

Related Features and Technologies

The OSPF Update Packet-Pacing Configurable Timers feature is an extension of the OSPF routing protocol. For more information about configuring OSPF, packet pacing, area border router (ABR) and autonomous system boundary router (ASBR) summarization, and stub router configuration, refer to the Release 12.2 Cisco IOS IP Routing Configuration Guide and the Cisco IOS IP Command Reference, Volume 2 of 3: Routing Protocols.

Supported Platforms

The OSPF Update Packet-Pacing Configurable Timers feature is supported by the following platforms in Cisco IOS Release 12.2(14)S that support OSPF:

•Cisco 7200 series

•Cisco 7400 series

•Cisco 7500 series

Determining Platform Support Through Cisco Feature Navigator

Cisco IOS software is packaged in feature sets that support 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:

http://www.cisco.com/go/fn

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 RFCs are supported by this feature.

Configuration Tasks

See the following sections for configuration tasks for the OSPF Update Packet-Pacing Configurable Timers feature. Each task in the list is identified as either required or optional:

•Configuring OSPF Packet-Pacing Timers (required)

•Verifying OSPF Packet-Pacing Timers (optional)

Configuring OSPF Packet-Pacing Timers

To configure a flood packet pacing timer, use the following commands beginning in router configuration mode:

 
Command
Purpose

Step 1 

Router(config)# router ospf process-id

Places the router in router configuration mode and enables an OSPF routing process.

Step 2 

Router(config-router)# timers pacing flood milliseconds

Configures a flood packet pacing timer delay (in milliseconds).

To configure a retransmission packet pacing timer, use the following commands beginning in router configuration mode:

 
Command
Purpose

Step 1 

Router(config)# router ospf process-id

Places the router in router configuration mode and enables an OSPF routing process.

Step 2 

Router(config-router)# timers pacing retransmission milliseconds

Configures a retransmission packet pacing timer delay (in milliseconds).

To configure a group packet pacing timer, use the following commands beginning in router configuration mode:

 
Command
Purpose

Step 1 

Router(config)# router ospf process-id

Places the router in router configuration mode and enables an OSPF routing process.

Step 2 

Router(config-router)# timers pacing lsa-group seconds

Configures an LSA group packet pacing timer delay (in seconds).

Verifying OSPF Packet-Pacing Timers

To verify that OSPF packet pacing has been configured, use the show ip ospf privileged EXEC command. The output of the show ip ospf command will display the type and delay time of the configurable pacing timers (flood, retransmission, group). The following example output is from the show ip ospf command: 

Router# show ip ospf 

  Routing Process "ospf 1" with ID 10.0.0.1 and Domain ID 10.20.0.1 

  Supports only single TOS(TOS0) routes 

  Supports opaque LSA 

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

  Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs 

  LSA group pacing timer 100 secs 

  Interface flood pacing timer 55 msecs 

  Retransmission pacing timer 100 msecs 

  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 message digest authentication 

         SPF algorithm executed 4 times 

         Area ranges are 

         Number of LSA 4. Checksum Sum 0x29BEB  

         Number of opaque link LSA 0. Checksum Sum 0x0      

         Number of DCbitless LSA 3 

         Number of indication LSA 0 

         Number of DoNotAge LSA 0 

         Flood list length 0 

     Area 172.16.26.0 

         Number of interfaces in this area is 0 

         Area has no authentication 

         SPF algorithm executed 1 times 

         Area ranges are 

            192.168.0.0/16 Passive Advertise  

         Number of LSA 1. Checksum Sum 0x44FD   

         Number of opaque link LSA 0. Checksum Sum 0x0      

         Number of DCbitless LSA 1 

         Number of indication LSA 1 

         Number of DoNotAge LSA 0 

         Flood list length 0

Troubleshooting Tips

If the number of OSPF packet retransmissions rapidly increases, increase the value of the packet pacing timers. The number of OSPF packet retransmissions is displayed in the output of the show ip ospf neighbor command.

Monitoring and Maintaining OSPF Packet-Pacing Timers

To monitor and maintain OSPF packet-pacing timers, use the following commands in privileged EXEC mode:

Command
Purpose

Router# show ip ospf

Displays general information about OSPF routing processes.

router# show ip ospf neighbor

Displays OSPF neighbor information on a per-interface basis.

Router# clear ip ospf redistribution

Clears route redistribution based on the OSPF routing process ID.


Configuration Examples

This section provides the following configuration examples:

•Flood Pacing Example

•Retransmission Pacing Example

•Group Pacing Example

Flood Pacing Example

The following example configures LSA flood pacing updates to occur in 50-millisecond intervals for OSPF routing process 1: 

Router(config)# router ospf 1

Router(config-router)# timers pacing flood 50

Retransmission Pacing Example

The following example configures LSA flood pacing updates to occur in 100-millisecond intervals for OSPF routing process 1: 

Router(config)# router ospf 1

Router(config-router)# timers pacing retransmission 100

Group Pacing Example

The following example configures OSPF group pacing updates between LSA groups to occur in 75-second intervals for OSPF routing process 1: 

Router(config)# router ospf 1

Router(config-router)# timers pacing lsa-group 75

Command Reference

The following commands are introduced or modified in the feature or features documented in this module. For information about these commands, see the Cisco IOS IP Routing Protocols Command Reference at http://www.cisco.com/en/US/docs/ios/iproute/command/reference/irp_book.html. For information about all Cisco IOS commands, go to the Command Lookup Tool at http://tools.cisco.com/Support/CLILookup or to the Cisco IOS Master Commands List.

•timers pacing flood

•timers pacing lsa-group

•timers pacing retransmission

•show ip ospf

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