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Cisco IOS Software Releases 12.0 S

IS-IS Fast-Flooding of LSPs Using the fast-flood Command

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IS-IS Fast-Flooding of LSPs Using the fast-flood Command

Table Of Contents

IS-IS Fast-Flooding of LSPs Using the fast-flood Command

Contents

Information About IS-IS Fast-Flooding of LSPs Using the fast-flood Command

Benefits of Fast-Flooding

How to Use the IS-IS Fast-Flooding of LSPs Using the fast-flood Command Feature

Enabling Fast-Flooding

Additional References

Related Documents

Standards

MIBs

RFCs

Technical Assistance

Command Reference

fast-flood


IS-IS Fast-Flooding of LSPs Using the fast-flood Command


The IS-IS Fast-Flooding of LSPs Using the fast-flood Command feature improves Intermediate System-to-Intermediate System (IS-IS) convergence time when new link-state packets (LSPs) are generated in the network and shortest path first (SPF) is triggered by the new LSPs. This document introduces the new fast-flood command.

Feature History for the IS-IS Fast-Flooding of LSPs Using the fast-flood Command Feature

Release
Modification

12.0(27)S

This feature was introduced.

12.3(7)T

This feature was integrated into Cisco IOS Release 12.3(7)T.



Note Software images for Cisco 12000 series Internet routers have been deferred to Cisco IOS Release 12.0(27)S1.


Finding Support Information for Platforms and Cisco IOS Software Images

Use Cisco Feature Navigator to find information about platform support and Cisco IOS software image support. Access Cisco Feature Navigator at http://www.cisco.com/go/fn. You must have an account on Cisco.com. If you do not have an account or have forgotten your username or password, click Cancel at the login dialog box and follow the instructions that appear.

Contents

Information About IS-IS Fast-Flooding of LSPs Using the fast-flood Command

How to Use the IS-IS Fast-Flooding of LSPs Using the fast-flood Command Feature

Additional References

Command Reference

Information About IS-IS Fast-Flooding of LSPs Using the fast-flood Command

Before using the fast-flood command, you should understand the concept in the following section:

Benefits of Fast-Flooding

Benefits of Fast-Flooding

If you are using the SPF and if very short values are used for the initial delay required (less than 40 milliseconds), SPF may start before the LSP that triggered SPF is flooded to neighbors. The router should always flood (at least) the LSP that triggered SPF before the router runs the SPF computation.

We recommend that you enable the fast-flooding of LSPs before the router runs the SPF computation, to ensure that the whole network achieves a faster convergence time.

How to Use the IS-IS Fast-Flooding of LSPs Using the fast-flood Command Feature

This section contains the following procedure:

Enabling Fast-Flooding (optional)

Enabling Fast-Flooding

Perform this task to enable fast-flooding.

SUMMARY STEPS

1. enable

2. configure terminal

3. router isis [tag]

4. fast-flood lsp-number

5. end

6. show running-configuration

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 isis tag

Example:

Router(config)# router isis first

Configures an IS-IS routing process and enters router configuration mode.

Step 4 

fast-flood lsp-number

Example:

Router(config-router)# fast-flood 12

Fast-floods LSPs.

Step 5 

end

Example:

Router(config-router)# end

Exits router configuration mode.

Step 6 

show running-configuration

Example:

Router(config)# show running-configuration

Verifies that fast-flooding has been enabled.

Additional References

The following sections provide references related to the IS-IS Fast-Flooding of LSPs Using the fast-flood Command feature.

Related Documents

Related Topic
Document Title

IS-IS commands

"Integrated IS-IS Commands" chapter in the Cisco IOS IP Command Reference, Volume 2 of 3: Routing Protocols, Release 12.3 T

IS-IS configuration tasks

"Configuring Integrated IS-IS" chapter in the Cisco IOS IP Configuration Guide


Standards

Standards
Title

None


MIBs

MIBs
MIBs Link

None

To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:

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


RFCs

RFCs
Title

RFC 2328

OSPF Version 2


Technical Assistance

Description
Link

Technical Assistance Center (TAC) home page, containing 30,000 pages of searchable technical content, including links to products, technologies, solutions, technical tips, and tools. Registered Cisco.com users can log in from this page to access even more content.

http://www.cisco.com/public/support/tac/home.shtml


Command Reference

This section documents the new fast-flood command:

fast-flood

To fast-flood Intermediate System-to-Intermediate System (IS-IS) link-state packets (LSPs), use the fast-flood command in router configuration mode. To disable the fast-flooding, use the no version of this command.

fast-flood lsp-number

no fast-flood lsp-number

Syntax Description

lsp-number

(Optional) The number of LSPs from 1 to 15 to be flooded before shortest path first (SPF) is started. The default is 5 LSPs.


Defaults

Fast-flooding is disabled. Five LSPs are flooded before SPF is started.

Command Modes

Router configuration

Command History

Release
Modification

12.0(27)S

This command was introduced.

12.3(7)T

This command was integrated into Cisco IOS Release 12.3(7)T.


Usage Guidelines

The fast-flood command tells the router to flood a certain number of LSPs, as configured by the lsp-number argument (if no lsp-number value has been specified, the default value of 5 is used), that invoke SPF before running SPF. When you speed up the LSP flooding process, you improve overall network convergence time.

If you are running SPF and if you have configured very short values (less than 40 milliseconds) for the initial delay that is set by the seconds argument of the incremental-spf command, the SPF computation might start before the LSP that triggered SPF is flooded to neighbors. The router should always flood (at least) the LSP that triggered SPF before the router runs the SPF computation.

We recommend that you enable the fast-flooding of LSPs before the router runs the SPF computation, in order to achieve a faster convergence time.

Examples

In the following example, the fast-flood command is entered to configure the router to flood the first seven LSPs that invoke SPF, before the SPF computation is started. When the show running-configuration command is entered, the output confirms that fast-flooding has been enabled on the router.

Router# clear isis rib redistribution 10.1.0.0 255.255.0.0
Router> enable
Router# configure terminal
Router(config)# router isis first
Router(config-router)# fast-flood 7
Router(config-router)# end
Router# show running-configuration

fast-flood 7

Related Commands

Command
Description

incremental-spf

Enables incremental SPF.