Cisco IOS XE IP Routing Protocols Configuration Guide, Release 2
OSPF Incremental SPF
Download this chapter
OSPF Incremental SPFOSPF Incremental SPF
give_us_feedback

Table Of Contents

OSPF Incremental SPF

Finding Feature Information

Contents

Prerequisites for OSPF Incremental SPF

Information About OSPF Incremental SPF

Benefits of OSPF Incremental SPF

How to Enable OSPF Incremental SPF

Enabling Incremental SPF

Configuration Examples for OSPF Incremental SPF

Incremental SPF: Example

Additional References

Related Documents

Standards

MIBs

RFCs

Technical Assistance

Feature Information for OSPF Incremental SPF


OSPF Incremental SPF

Last Updated: May 4, 2009

The Open Shortest Path First (OSPF) protocol can be configured to use an incremental SPF algorithm for calculating the shortest path first routes. Incremental SPF is more efficient than the full SPF algorithm, thereby allowing OSPF to converge faster on a new routing topology in reaction to a network event.

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 Incremental SPF" 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

•Prerequisites for OSPF Incremental SPF

•Information About OSPF Incremental SPF

•How to Enable OSPF Incremental SPF

•Configuration Examples for OSPF Incremental SPF

•Additional References

•Feature Information for OSPF Incremental SPF

Prerequisites for OSPF Incremental SPF

It is presumed that you have OSPF configured in your network.

Information About OSPF Incremental SPF

Before you enable OSPF Incremental SPF, you should understand the following concept:

•Benefits of OSPF Incremental SPF

Benefits of OSPF Incremental SPF

OSPF uses Dijkstra's SPF algorithm to compute the shortest path tree (SPT). During the computation of the SPT, the shortest path to each node is discovered. The topology tree is used to populate the routing table with routes to IP networks. When changes to a Type-1 or Type-2 link-state advertisement (LSA) occur in an area, the entire SPT is recomputed. In many cases, the entire SPT need not be recomputed because most of the tree remains unchanged. Incremental SPF allows the system to recompute only the affected part of the tree. Recomputing only a portion of the tree rather than the entire tree results in faster OSPF convergence and saves CPU resources. Note that if the change to a Type-1 or Type-2 LSA occurs in the calculating router itself, then the full SPT is performed.

Incremental SPF is scheduled in the same way as the full SPF. Routers enabled with incremental SPF and routers not enabled with incremental SPF can function in the same internetwork.

How to Enable OSPF Incremental SPF

This section contains the following procedure:

•Enabling Incremental SPF

Enabling Incremental SPF

This section describes how to enable incremental SPF.

SUMMARY STEPS

1. enable

2. configure terminal

3. router ospf process-id

4. ispf

5. end

DETAILED STEPS

 
Command or Action
Purpose

Step 1 

enable

Example:

Router> enable

Enables 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 

ispf

Example:

Router(config-router)# ispf

Enables incremental SPF.

Step 5 

end

Example:

Router(config-router)# end

Exits router configuration mode.

Configuration Examples for OSPF Incremental SPF

This section contains an example of configuring OSPF incremental SPF:

•Incremental SPF: Example

Incremental SPF: Example

This example enables incremental SPF: 

router ospf 1

 ispf

Additional References

The following sections provide references related to OSPF Incremental SPF.

Related Documents

Related Topic
Document Title

OSPF commands

Cisco IOS IP Routing Protocols Command Reference

Configuring OSPF

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

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 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 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/public/support/tac/home.shtml


Feature Information for OSPF Incremental SPF

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 Incremental SPF

Feature Name
Releases
Feature Information

OSPF Incremental SPF

Cisco IOS XE
Release 2.1

OSPF can be configured to use an incremental SPF algorithm for calculating the shortest path first routes. Incremental SPF is more efficient than the full SPF algorithm, thereby allowing OSPF to converge faster on a new routing topology in reaction to a network event

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

•ispf


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.