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Implementing Selective Packet Discard in IPv6
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Implementing Selective Packet Discard in IPv6

Table Of Contents

Implementing Selective Packet Discard in IPv6

Finding Feature Information

Contents

Information About Implementing Selective Packet Discard in IPv6

SPD in IPv6-Overview

SPD State Check

SPD Mode

SPD Headroom

How to Implement Selective Packet Discard in IPv6

Configuring the SPD Process Input Queue

Configuring SPD Mode

Configuring SPD Headroom

Configuration Examples for Implementing Selective Packet Discard in IPv6

Example: Configuring the SPD Process Input Queue

Additional References

Related Documents

Standards

MIBs

RFCs

Technical Assistance

Feature Information for Implementing Selective Packet Discard in IPv6


Implementing Selective Packet Discard in IPv6


First Published: February 26, 2010
Last Updated: February 26, 2010

This document describes the Selective Packet Discard (SPD) feature in IPv6. The SPD feature in IPv6 manages the process level input queues on the Route Processor (RP). SPD provides priority to routing protocol packets and other important traffic control Layer 2 keepalives during periods of process level queue congestion.

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 for Implementing Selective Packet Discard in IPv6" section.

Use Cisco Feature Navigator to find information about platform support and Cisco 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

Information About Implementing Selective Packet Discard in IPv6

How to Implement Selective Packet Discard in IPv6

Configuration Examples for Implementing Selective Packet Discard in IPv6

Additional References

Feature Information for Implementing Selective Packet Discard in IPv6

Information About Implementing Selective Packet Discard in IPv6

SPD in IPv6-Overview

SPD in IPv6-Overview

The SPD mechanism manages the process level input queues on the RP. SPD provides priority to routing protocol packets and other important traffic control Layer 2 keepalives during periods of process level queue congestion.

SPD State Check

The SPD state check is performed on the IPv6 process input queue on the RP. High-priority packets, such as those of IP precedence 7, are not applied to SPD and are never dropped. All remaining packets, however, can be dropped depending on the length of the IPv6 packet input queue and the SPD state. The possible SPD states are as follows:

Normal: The process input queue is less than the SPD minimum threshold.

Random drop: The process input queue is between the SPD minimum and maximum thresholds.

Max: The process input queue is equal to the SPD maximum threshold.

The size of the process input queue governs the SPD state: normal (no drop), random drop, or max. When the process input queue is less than the SPD minimum threshold, SPD takes no action and enters normal state. In the normal state, no packets are dropped. When the input queue reaches the maximum threshold, SPD enters max state, in which normal priority packets are discarded. If the input queue is between the minimum and maximum thresholds, SPD enters the random drop state, in which normal packets may be dropped.

SPD Mode

Three IPv6 SPD modes are supported: none (which is the default), aggressive drop, and OSPF mode. The aggressive drop mode discards incorrectly formatted packets when the IPv6 is in the random drop state. OSPF mode provides a mechanism whereby OSPF packets are handled with SPD priority.

SPD Headroom

With SPD, the behavior of normal IPv6 packets is not changed. However, routing protocol packets are given higher priority, because SPD recognizes routing protocol packets by the IPv6 precedence field. Therefore, if the IPv6 precedence is set to 7, then the packet is given priority.

SPD prioritizes IPv6 packets with a precedence of 7 by allowing the Cisco IOS software to queue them into the process level input queue above the normal input queue limit. The number of packets allowed in excess of the normal limit is called the SPD headroom. The SPD headroom default is 100, which means that a high precedence packet is not dropped if the size of the input hold queue is lower than 175 (which is the input queue default size + SPD headroom size).

Because Interior Gateway Protocols (IGPs) and link stability are tenuous and crucial, such packets are given the highest priority and are given extended SPD headroom with a default of 10 packets. These packets are not dropped if the size of the input hold queue is lower than 185 (input queue default size + SPD headroom size + SPD extended headroom).

Non-IPv6 packets such as Connectionless Network Service Intermediate System-to-Intermediate System (CLNS IS-IS) packets, PPP packets, and High-Level Data Link Control (HDLC) keepalives are treated as normal priority as a result of being Layer 2 instead of Layer 3. In addition, IGPs operating at Layer 3 or higher are given priority over normal IPv6 packets, but are given the same priority as Border Gateway Protocol (BGP) packets. Therefore, during BGP convergence or during times of very high BGP activity, IGP hellos and keepalives often are dropped, causing IGP adjacencies to fail.

How to Implement Selective Packet Discard in IPv6

Configuring the SPD Process Input Queue (required)

Configuring SPD Mode (optional)

Configuring SPD Headroom (optional)

Configuring the SPD Process Input Queue

SUMMARY STEPS

1. enable

2. configure terminal

3. ipv6 spd queue max-threshold value

4. ipv6 spd queue min-threshold value

5. exit

6. show ipv6 spd

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 

ipv6 spd queue max-threshold value

Example:
Router(config)# ipv6 spd queue max-threshold 
60000

Configures the maximum number of packets in the SPD process input queue.

Step 4 

ipv6 spd queue min-threshold value

Example:
Router(config)# ipv6 spd queue max-threshold 
4094

Configures the minimum number of packets in the IPv6 SPD process input queue.

Step 5 

exit

Example:

Router(config)# exit

Returns the router to privileged EXEC mode.

Step 6 

show ipv6 spd

Example:

Router# show ipv6 spd

Displays IPv6 SPD configuration.

Configuring SPD Mode

No IPv6 SPD mode is configured by default. However, you may want to configure the router to use a specific mode when the router enters a specified IPv6 SPD state or to prioritize certain packets.

SUMMARY STEPS

1. enable

2. configure terminal

3. ipv6 spd mode {aggressive | ospf}

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 

ipv6 spd mode {aggressive | ospf}

Example:

Router(config)# ipv6 spd mode aggressive

Configures an IPv6 SPD mode.

Configuring SPD Headroom

SUMMARY STEPS

1. enable

2. configure terminal

3. spd headroom value

4. spd extended-headroom size

5. exit

6. show ipv6 spd

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 

spd headroom size
Example:

Router(config)# spd headroom 200

Configures SPD headroom.

Step 4 

spd extended-headroom size
Example:

Router(config)# spd extended-headroom 11

Configures extended SPD headroom.

Step 5 

exit

Example:

Router(config)# exit

Returns the router to privileged EXEC mode.

Step 6 

show ipv6 spd

Example:

Router# show ipv6 spd

Displays the IPv6 SPD configuration.

Configuration Examples for Implementing Selective Packet Discard in IPv6

Example: Configuring the SPD Process Input Queue

Example: Configuring the SPD Process Input Queue

The following example shows the SPD process input queue configuration. The maximum process input queue threshold is 60,000, and the SPD state is normal. The headroom and extended headroom values are the default:

Router# ipv6 spd queue max-threshold 5000
Router# show ipv6 spd 

Current mode: normal 
Queue max threshold: 60000, Headroom: 100, Extended Headroom: 10 
IPv6 packet queue: 0 

Additional References

Related Documents

Related Topic
Document Title

IPv6 supported feature list

Start Here: Cisco IOS Software Release Specifics for IPv6 Features, Cisco IOS XE IPv6 Configuration Guide

IPv6 commands: complete command syntax, command mode, defaults, usage guidelines, and examples

Cisco IOS IPv6 Command Reference

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

None

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

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


RFCs

RFC
Title

RFC 2474

Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers


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.

http://www.cisco.com/cisco/web/support/index.html


Feature Information for Implementing Selective Packet Discard in IPv6

Table 1 lists the features in this module and provides links to specific configuration information.

Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which 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 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.


Table 1 Feature Information for Implementing Selective Packet Discard in IPv6 

Feature Name
Releases
Feature Information

IPv6 Selective Packet Discard

Cisco IOS XE Release 2.6

The SPD mechanism manages the process level input queues on the RP. SPD provides priority to routing protocol packets and other important traffic control Layer 2 keepalives during periods of process level queue congestion.

The following commands were introduced or modified: ipv6 spd mode, ipv6 spd queue max-threshold, ipv6 spd queue min-threshold, show ipv6 spd, spd extended-headroom, spd headroom.