IP Routing: ISIS Configuration Guide, Cisco IOS XE Release 3S (Cisco ASR 1000)
Overview of IS-IS Fast Convergence
Overview of IS-IS Fast Convergence
Last Updated: December 4, 2012
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
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.
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:
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:
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:
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:
To enhance IS-IS network security, see the "Enhancing Security in an IS-IS Network" module.
Feature Information for Overview of IS-IS Fast Convergence
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.
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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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