iproute_ospf

OSPF Update Packet-Pacing Configurable Timers

This module describes the OSPF Update Packet-Pacing Configurable Timers feature, which allows you to configure the rate at which OSPF LSA flood pacing, retransmission pacing, and group pacing updates occur.

Finding Feature Information

For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the "Feature Information for OSPF Update Packet-Pacing Configurable Timers" section.

Use Cisco Feature Navigator to find information about platform support and Cisco IOS XE software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.

Contents

•Restrictions on OSPF Update Packet-Pacing Configurable Timers

•Information About OSPF Update Packet-Pacing Configurable Timers

•How to Configure OSPF Packet-Pacing Timers

•Configuration Examples of OSPF Update Packet-Pacing

•Additional References

•Feature Information for OSPF Update Packet-Pacing Configurable Timers

Restrictions on OSPF Update Packet-Pacing Configurable Timers

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 that are associated with changing the default timer values.

Information About OSPF Update Packet-Pacing Configurable Timers

Before you change the OSPF update packet-pacing timers, you should understand the following concepts:

•Functionality of the OSPF Update Packet-Pacing Timers

•Benefits of OSPF Update Packet-Pacing Configurable Timers

Functionality of the OSPF Update Packet-Pacing Timers

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 XE 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 that is used for group LSA refreshment; however, this timer does not change the frequency at which individual LSAs are refreshed (the default refresh occurs every 30 minutes).

Caution 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 of OSPF Update Packet-Pacing Configurable Timers

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.

How to Configure OSPF Packet-Pacing Timers

The tasks in this section describe how to configure and verify three OSPF update packet-pacing timers.

•Configuring OSPF Packet-Pacing Timers (required)

•Verifying OSPF Packet-Pacing Timers (optional)

•Monitoring and Maintaining OSPF Packet-Pacing Timers (optional)

Configuring OSPF Packet-Pacing Timers

Caution 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.

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

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

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

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 sample 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

Configuration Examples of OSPF Update Packet-Pacing

This section provides the following configuration examples:

•Example: LSA Flood Pacing

•Example: LSA Retransmission Pacing

•Example: LSA Group Pacing

Example: LSA Flood Pacing

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

Example: LSA Retransmission Pacing

The following example configures LSA retransmission 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

Example: LSA Group Pacing

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

Additional References

For additional information related to the OSPF Update Packet-Pacing Configurable Timers feature, see the following references:

Related Documents

Standards

MIBs

RFCs

Technical Assistance

Feature Information for OSPF Update Packet-Pacing Configurable Timers

Table 1 lists the release history for this feature.

Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which Cisco IOS XE software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.

Note Table 1 lists only the Cisco IOS XE software release that introduced support for a given feature in a given Cisco IOS XE software release train. Unless noted otherwise, subsequent releases of that Cisco IOS XE software release train also support that feature.

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Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental.

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