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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: August 21, 2007Last Updated: November 18, 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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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
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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.
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DETAILED STEPS
Configuring an SPD Mode
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DETAILED STEPS
Configuring SPD Headroom
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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 1, and the SPD state is normal. The headroom and extended headroom values are set to the default.
Router# ipv6 spd queue max-threshold 1Router# show ipv6 spdCurrent mode: normalQueue max threshold: 1, 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 IPv6 Configuration Guide
IPv6 commands: complete command syntax, command mode, command history, defaults, usage guidelines, and examples
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
RFC 4594
Configuration Guidelines for DiffServ Service Classes
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
Table 1 Feature Information for Implementing Selective Packet Discard in IPv6
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:
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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)SThe 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:
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The following commands were introduced or modified: ipv6 spd queue max-threshold, show ipv6 spd, spd extended-headroom, spd headroom.
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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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