IP Routing: OSPF Configuration Guide, Cisco IOS XE Release 3S (Cisco ASR 1000)
OSPF Update Packet-Pacing Configurable Timers
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OSPF Update Packet-Pacing Configurable Timers

Contents

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

Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and 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 table at the end of this module.

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

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

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


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:
SUMMARY STEPS

    1.    Router(config)# router ospf process-id

    2.    Router(config-router)# timers pacing flood milliseconds


DETAILED STEPS
     Command or ActionPurpose
    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).

     

    Configuring a Retransmission Packet-Pacing Timer

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

    SUMMARY STEPS

      1.    Router(config)# router ospf process-id

      2.    Router(config-router)# timers pacing retransmission milliseconds


    DETAILED STEPS
       Command or ActionPurpose
      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).

       

      Configuring a Group Packet-Pacing Timer

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

      SUMMARY STEPS

        1.    Router(config)# router ospf process-id

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


      DETAILED STEPS
         Command or ActionPurpose
        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 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

        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 of OSPF Update Packet-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

        Related Topic

        Document Title

        Configuring OSPF

        "Configuring OSPF"

        OSPF commands

        Cisco IOS IP Routing: OSPF Command Reference

        Cisco IOS master command list, all releases

        Cisco IOS Master Command List, All Releases

        Standards

        Standard

        Title

        No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.

        --

        MIBs

        MIB

        MIBs Link

        No new or modified MIBs are supported by this feature, and support for existing MIBs has not been modified by this feature.

        To locate and download MIBs for selected platforms, Cisco IOS XE software releases , and feature sets, use Cisco MIB Locator found at the following URL:

        http:/​/​www.cisco.com/​go/​mibs

        RFCs

        RFC

        Title

        No new or modified RFCs are supported by this feature, and support for existing RFCs has not been modified by this feature.

        --

        Technical Assistance

        Description

        Link

        The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password.

        http:/​/​www.cisco.com/​cisco/​web/​support/​index.html

        Feature Information for OSPF Update Packet-Pacing Configurable Timers

        The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.

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

        Table 1 Feature Information for OSPF Update Packet-Pacing Configurable Timers

        Feature Name

        Releases

        Feature Information

        OSPF Update Packet-Pacing Configurable Timers

        Cisco IOS XE Release 2.1

        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.

        The following commands are introduced or modified in the feature documented in this module:

        • timers pacing flood
        • timers pacing lsa-group
        • timers pacing retransmission
        • show ip ospf