Table Of Contents

Overview of IS-IS Fast Convergence

Finding Feature Information

Contents

Prerequisites for IS-IS Fast Convergence

Information About IS-IS Fast Convergence

Network Convergence

Design Recommendations for Achieving Faster Network Convergence

Where to Go Next

Additional References

Related Documents

Standards

MIBs

RFCs

Technical Assistance

Feature Information for Overview of IS-IS Fast Convergence

Overview of IS-IS Fast Convergence

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First Published: November 30, 2007

Last Updated: May 4, 2009

This module provides information about the topics of Intermediate System-to-Intermediate System (IS-IS) fast convergence. The tasks in the modules that follow this overview can help you improve convergence times for IS-IS networks.

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 Overview of IS-IS Fast Convergence" 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 IS-IS Fast Convergence

•Information About IS-IS Fast Convergence

•Where to Go Next

•Additional References

•Feature Information for Overview of IS-IS Fast Convergence

Prerequisites for IS-IS Fast Convergence

You should be familiar with the concepts described in the "Integrated IS-IS Routing Protocol Overview" module.

Information About IS-IS Fast Convergence

You should understand the following concepts before you configure any features to improve IS-IS network convergence times:

•Network Convergence

•Design Recommendations for Achieving Faster Network Convergence

Network Convergence

Convergence is the process of all routers coming to agreement on optimal routes in a network. When a network event causes routes to become available or unavailable, routers send routing update messages through the network that cause routing algorithms to recalculate optimal routes. Eventually all the routers agree on the routes as well as the network topology. Fast convergence benefits network performance. Routing algorithms that converge slowly may cause temporary routing loops or temporary network unavailability.

The process of network convergence can be divided into three separate stages:

1. Routing change detection: The speed at which a device on the network can detect and react to the failure or modification of one of its own components, or to a topology change caused by the failure or modification of a component on a routing protocol peer.

2. Routing change notification: The speed at which the failure or topology change in the previous stage can be communicated to other devices in the network.

3. Alternate path calculation: The speed at which all devices on the network, having been notified of the failure or topology change, can process the information and calculate an alternate path through which data can flow.

An improvement in any one of these stages provides an improvement in overall convergence. In addition to a basic configuration task that is recommended as a first step in configuring an IS-IS router with best practice parameters for achieving fast convergence, several recommended configuration tasks are grouped according to the stage of network convergence they can improve. For more information, see the following modules:

•"Setting Best Practice Parameters for IS-IS Fast Convergence"

•"Reducing Failure Detection Times in IS-IS Networks"

•"Reducing Link Failure and Topology Change Notification Times in IS-IS Networks"

•"Reducing Alternate-Path Calculation Times in IS-IS Networks"

Design Recommendations for Achieving Faster Network Convergence

A faster processor can provide better performance for network convergence.

Where to Go Next

To configure features to improve IS-IS network convergence times, complete the optional tasks in one or more of the following modules:

•"Setting Best Practice Parameters for IS-IS Fast Convergence"

•"Reducing Failure Detection Times in IS-IS Networks"

•"Reducing Alternate-Path Calculation Times in IS-IS Networks"

To enhance IS-IS network security, see the "Enhancing Security in an IS-IS Network" module.

Additional References

The following sections provide references related to IS-IS configuration tasks to achieve fast convergence.

Related Documents

Related Topic	Document Title
IS-IS commands: complete command syntax, command mode, defaults, command history, usage guidelines, and examples	Cisco IOS IP Routing Protocols Command Reference
Overview of Cisco IS-IS conceptual information with links to all the individual IS-IS modules	"Integrated IS-IS Routing Protocol Overview"
Cisco IOS master command list, all  releases	Cisco IOS Master Command List, All Releases

Standards

Standard	Title
ISO 8473	CLNP, Connectionless Network Protocol
ISO 9542	ES-IS Routing Information Exchange Protocol
ISO/IEC 10589	IS-IS Protocol

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 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 Overview of IS-IS Fast Convergence

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.

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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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Table 1 Feature Information for Overview of IS-IS Fast Convergence

Feature Name	Releases	Feature Information
Overview of IS-IS Fast Convergence	Cisco IOS XE Release 2.1	This feature was introduced on the Cisco ASR 1000 Series Aggregation Services Routers.

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