Cisco IOS XE IP Routing Protocols Configuration Guide, Release 2
OSPF Shortest Path First Throttling
Download this chapter
OSPF Shortest Path First ThrottlingOSPF Shortest Path First Throttling
give_us_feedback

Table Of Contents

OSPF Shortest Path First Throttling

Finding Feature Information

Contents

Information About OSPF SPF Throttling

Shortest Path First Calculations

How to Configure OSPF SPF Throttling

Configuring OSPF SPF Throttling

Verifying SPF Throttle Values

Configuration Example for OSPF SPF Throttling

Throttle Timers: Example

Additional References

Related Documents

Standards

MIBs

RFCs

Technical Assistance

Feature Information for OSPF Shortest Path First Throttling


OSPF Shortest Path First Throttling

Last Updated: May 4, 2009

The OSPF Shortest Path First Throttling feature makes it possible to configure shortest path first (SPF) scheduling in millisecond intervals and to potentially delay SPF calculations during network instability. SPF is scheduled to calculate the Shortest Path Tree (SPT) when there is a change in topology. One SPF run may include multiple topology change events.

The interval at which the SPF calculations occur is chosen dynamically and is based on the frequency of topology changes in the network. The chosen interval is within the boundary of the user-specified value ranges. If the network topology is unstable, SPF throttling calculates SPF scheduling intervals to be longer until the topology becomes stable.

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 Shortest Path First Throttling" 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

•Information About OSPF SPF Throttling

•How to Configure OSPF SPF Throttling

•Configuration Example for OSPF SPF Throttling

•Additional References

•Feature Information for OSPF Shortest Path First Throttling

Information About OSPF SPF Throttling

Before using SPF throttling, you should understand the following concept:

•Shortest Path First Calculations

Shortest Path First Calculations

SPF calculations occur at the interval set by the timers throttle spf command. The wait interval indicates the amount of time to wait until the next SPF calculation occurs. Each wait interval after that calculation is twice as long as the previous one until the wait interval reaches the maximum wait time specified.

The SPF timing can be better explained using an example. In this example the start interval is set at 5 milliseconds (ms), the wait interval at 1000 milliseconds, and the maximum wait time is set at 90,000 milliseconds. 

timers throttle spf 5 1000 90000

Figure 1 shows the intervals at which the SPF calculations occur so long as at least one topology change event is received in a given wait interval.

Figure 1 SPF Calculation Intervals Set by the timers throttle spf Command

Notice that the wait interval between SPF calculations doubles when at least one topology change event is received during the previous wait interval. Once the maximum wait time is reached, the wait interval remains the same until the topology stabilizes and no event is received in that interval.

If the first topology change event is received after the current wait interval, the SPF calculation is delayed by the amount of time specified as the start interval. The subsequent wait intervals continue to follow the dynamic pattern.

If the first topology change event occurs after the maximum wait interval begins, the SPF calculation is again scheduled at the start interval and subsequent wait intervals are reset according the parameters specified in the timers throttle spf command. Notice in Figure 2 that a topology change event was received after the start of the maximum wait time interval and that the SPF intervals have been reset.

Figure 2 Timer Intervals Reset After a Topology Change Event

How to Configure OSPF SPF Throttling

Perform the following tasks to configure OSPF SPF throttling:

•Configuring OSPF SPF Throttling (required)

•Verifying SPF Throttle Values (optional)

Configuring OSPF SPF Throttling

Perform this task to configure OSPF SPF throttling.

SUMMARY STEPS

1. enable

2. configure terminal

3. router ospf process-id

4. timers throttle spf spf-start spf-hold spf-max-wait

5. end

DETAILED STEPS

 
Command or Action
Purpose

Step 1 

enable

Example:

Router> enable

Enables higher privilege levels, such as privileged EXEC mode.

•Enter your password if prompted.

Step 2 

configure terminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3 

router ospf process-id

Example:

Router(config)# router ospf 1

Configures an OSPF routing process.

Step 4 

timers throttle spf spf-start spf-hold spf-max-wait

Example:

Router(config-router)# timers throttle spf 10 4800 90000

Sets OSPF throttling timers.

Step 5 

end

Example:

Router(config-router)# end

Exits configuration mode.


Verifying SPF Throttle Values

To verify SPF throttle timer values, use the show ip ospf command. The values are displayed in the lines that begin, "Initial SPF schedule delay...," "Minimum hold time between two consecutive SPFs...," and "Maximum wait time between two consecutive SPFs...." 

Router# show ip ospf


 Routing Process "ospf 1" with ID 10.10.10.2 and Domain ID 0.0.0.1

 Supports only single TOS(TOS0) routes

 Supports opaque LSA

 It is an autonomous system boundary router

 Redistributing External Routes from,

    static, includes subnets in redistribution

Initial SPF schedule delay 5 msecs 

 Minimum hold time between two consecutive SPFs 1000 msecs 

 Maximum wait time between two consecutive SPFs 90000 msecs 

 Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs

 LSA group pacing timer 240 secs

 Interface flood pacing timer 33 msecs

 Retransmission pacing timer 66 msecs

 Number of external LSA 4. Checksum Sum 0x17445 

 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 1. 1 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 last executed 19:11:15.140 ago 

        SPF algorithm executed 28 times

        Area ranges are

        Number of LSA 4. Checksum Sum 0x2C1D4 

        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

Configuration Example for OSPF SPF Throttling

This section contains the following example:

•Throttle Timers: Example

Throttle Timers: Example

This example shows a router configured with the start, hold, and maximum interval values for the timers throttle spf command set at 5, 1,000, and 90,000 milliseconds, respectively. 

router ospf 1

 router-id 10.10.10.2

 log-adjacency-changes

 timers throttle spf 5 1000 90000 

 redistribute static subnets

 network 21.21.21.0 0.0.0.255 area 0

 network 22.22.22.0 0.0.0.255 area 00

Additional References

The following sections provide references related to OSPF Shortest Path First Throttling.

Related Documents

Related Topic
Document Title

Configuring OSPF

"Configuring OSPF" chapter in the Cisco IOS XE IP Routing Protocols Configuration Guide, Release 2

OSPF commands

Cisco IOS IP Routing Protocols Command Reference

Cisco IOS master command list, all releases

Cisco IOS Master Command List, All Releases


Standards

Standards
Title

None

—


MIBs

MIBs
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 releases, and feature sets, use Cisco MIB Locator found at the following URL:

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


RFCs

RFCs
Title

None

—


Technical Assistance

Description
Link

The Cisco Support website provides extensive online resources, including documentation and tools for troubleshooting and resolving technical issues with Cisco products and technologies.

To receive security and technical information about your products, you can subscribe to various services, such as the Product Alert Tool (accessed from Field Notices), the Cisco Technical Services Newsletter, and Really Simple Syndication (RSS) Feeds.

Access to most tools on the Cisco Support website requires a Cisco.com user ID and password.

http://www.cisco.com/techsupport


Feature Information for OSPF Shortest Path First Throttling

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.

Table 1 Feature Information for OSPF Shortest Path First Throttling 

Feature Name
Releases
Feature Information

OSPF Shortest Path First Throttling

Cisco IOS XE
Release 2.1

The OSPF Shortest Path First Throttling feature makes it possible to configure SPF scheduling in millisecond intervals and to potentially delay shortest path first (SPF) calculations during network instability. SPF is scheduled to calculate the Shortest Path Tree (SPT) when there is a change in topology.

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

•timer spf-interval

•timers throttle spf


CCDE, CCSI, CCENT, Cisco Eos, Cisco HealthPresence, the Cisco logo, Cisco Lumin, Cisco Nexus, Cisco Nurse Connect, Cisco Stackpower, Cisco StadiumVision, Cisco TelePresence, Cisco WebEx, DCE, and Welcome to the Human Network are trademarks; Changing the Way We Work, Live, Play, and Learn and Cisco Store are service marks; and Access Registrar, Aironet, AsyncOS, Bringing the Meeting To You, Catalyst, CCDA, CCDP, CCIE, CCIP, CCNA, CCNP, CCSP, CCVP, Cisco, the Cisco Certified Internetwork Expert logo, Cisco IOS, Cisco Press, Cisco Systems, Cisco Systems Capital, the Cisco Systems logo, Cisco Unity, Collaboration Without Limitation, EtherFast, EtherSwitch, Event Center, Fast Step, Follow Me Browsing, FormShare, GigaDrive, HomeLink, Internet Quotient, IOS, iPhone, iQuick Study, IronPort, the IronPort logo, LightStream, Linksys, MediaTone, MeetingPlace, MeetingPlace Chime Sound, MGX, Networkers, Networking Academy, Network Registrar, PCNow, PIX, PowerPanels, ProConnect, ScriptShare, SenderBase, SMARTnet, Spectrum Expert, StackWise, The Fastest Way to Increase Your Internet Quotient, TransPath, WebEx, and the WebEx logo are registered trademarks of Cisco Systems, Inc. and/or its affiliates in the United States and certain other countries.

All other trademarks mentioned in this document or website are the property of their respective owners. The use of the word partner does not imply a partnership relationship between Cisco and any other company. (0903R)

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, and 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.

© 2008-2009 Cisco Systems, Inc. All rights reserved.