- Integrated IS-IS Routing Protocol Overview
- Configuring a Basic IS-IS Network
- Customizing IS-IS for Your Network Design
- IS-IS MIB
- IS-IS Support for an IS-IS Instance per VRF for IP
- Overview of IS-IS Fast Convergence
- 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
- Enhancing Security in an IS-IS Network
Overview of IS-IS Fast Convergence
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 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 Table at the end of this document.
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:
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:
- 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.
- 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.
- 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:
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
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: ISIS 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 |
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: |
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. |
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.
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 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. |
Cisco and the Cisco logo are trademarks or registered trademarks of Cisco and/or its affiliates in the U.S. and other countries. To view a list of Cisco trademarks, go to this URL: www.cisco.com/go/trademarks. Third-party trademarks mentioned 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. (1110R)
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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