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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 an 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: August 21, 2007
Last Updated: November 18, 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 queue size is less than the maximum.

Full drop: The queue size is greater than or equal to the maximum.

In the normal state, the router never drops well-formed and malformed packets. In the full drop state, the router drops all well-formed and malformed packets.

SPD Mode

Users can enable an IPv6 SPD mode when the router reaches a certain SPD state. SPD aggressive drop mode drops deformed packets when IPv6 SPD is in random drop state. The OSPF mode allows OSPF packets to be handled with SPD priority.

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 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).

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 were treated as normal priority as a result of being Layer 2 instead of Layer 3. In addition, Interior Gateway Protocols (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. So, during BGP convergence or during times of very high BGP activity, IGP hellos and keepalives often were dropped, causing IGP adjacencies to fail.

Because IGP 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).

How to Implement Selective Packet Discard in IPv6

Configuring the SPD Process Input Queue

Configuring an SPD Mode

Configuring SPD Headroom

Configuring the SPD Process Input Queue

The SPD in IPv6 feature is enabled by default. Perform this task to configure the maximum and minimum number of packets in the IPv6 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 
100

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 min-threshold 4094

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

Note The minimum threshold value must be lower than the maximum threshold setting.

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 an SPD Mode

SUMMARY STEPS

1. enable

2. configure terminal

3. ipv6 spd mode {aggressive | tos protocol 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 | tos protocol ospf}

Example:

Router(config)# ipv6 spf mode aggressive

Configures an IPv6 SPD mode.

Configuring SPD Headroom

SUMMARY STEPS

1. enable

2. configure terminal

3. spd headroom size

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 1, and the SPD state is normal. The headroom and extended headroom values are set to the default.

Router# ipv6 spd queue max-threshold 1
Router# show ipv6 spd 

Current mode: normal 
Queue max threshold: 1, 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 IPv6 Configuration Guide

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

Cisco IOS IPv6 Command Reference


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

RFC 4594

Configuration Guidelines for DiffServ Service Classes


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 - Full Selective Packet Discard support

15.1(3)T

Users can now configure an IPv6 SPD mode when the router reaches a certain SPD state.

The following sections provide information about this feature:

SPD Mode

Configuring the SPD Process Input Queue

Configuring an SPD Mode

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

IPv6 Selective Packet Discard

12.2(33)SRC
12.2(33)SXH
15.0(1)S

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 sections provide information about this feature:

SPD in IPv6 Overview

Configuring the SPD Process Input Queue

Configuring SPD Headroom

Example: Configuring the SPD Process Input Queue

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