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Table Of Contents
Implementing Selective Packet Discard in IPv6
Information About Implementing Selective Packet Discard in IPv6
How to Implement Selective Packet Discard in IPv6
Configuring the SPD Process Input Queue
Configuration Examples for Implementing Selective Packet Discard in IPv6
Example: Configuring the SPD Process Input Queue
Feature Information for Implementing Selective Packet Discard in IPv6
Implementing Selective Packet Discard in IPv6
First Published: February 26, 2010Last Updated: February 26, 2010This 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
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Information About Implementing Selective Packet Discard in IPv6
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Information About Implementing Selective Packet Discard in IPv6
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:
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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
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Configuring the SPD Process Input Queue
SUMMARY STEPS
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DETAILED STEPS
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
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DETAILED STEPS
Configuring SPD Headroom
SUMMARY STEPS
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DETAILED STEPS
Configuration Examples for Implementing Selective Packet Discard in IPv6
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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 5000Router# show ipv6 spdCurrent mode: normalQueue max threshold: 60000, Headroom: 100, Extended Headroom: 10IPv6 packet queue: 0Additional References
Related Documents
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 master command list, all releases
Standards
No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.
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MIBs
None
To locate and download MIBs for selected platforms, Cisco software releases, and feature sets, use Cisco MIB Locator found at the following URL:
RFCs
RFC 2474
Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers
Technical Assistance
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
Cisco and the Cisco Logo are trademarks of Cisco Systems, Inc. and/or its affiliates in the U.S. and other countries. A listing of Cisco's trademarks can be found at 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. (1005R)
Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses. Any examples, command display output, and figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses in illustrative content is unintentional and coincidental.
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