 Feedback
|
Table Of Contents
QoS: L2 Overhead Specification for Shaping and Policing Parameters for Ethernet
Configuring QoS: L2 Overhead Specification for Shaping and Policing Parameters for Ethernet
hw-module slot qos account layer2 encapsulation
QoS: L2 Overhead Specification for Shaping and Policing Parameters for Ethernet
The Layer 2 (L2) Overhead Specification for Shaping and Policing Parameters for Ethernet allows you to configure shaping and policing bit rates that count Layer 2 encapsulation frame lengths in addition to Layer 3 packet lengths.
Feature History for QoS: L2 Overhead Specification for Shaping and Policing Parameters for Ethernet
12.0(28)S
This feature was introduced for the Cisco 12000 Series 4-Port Gigabit Ethernet ISE Line Card.
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
This document describes the L2 Overhead Specification feature in Cisco IOS 12.(28)S and includes the following sections:
•
Configuring QoS: L2 Overhead Specification for Shaping and Policing Parameters for Ethernet
Configuring QoS: L2 Overhead Specification for Shaping and Policing Parameters for Ethernet
This feature provides you with the option to configure shaping and policing QoS features that take the Layer 2 encapsulation overhead into account. Previously, outbound shaping and policing algorithms were based only on the Layer 3 packet length.
This feature is enabled with the hw-module slot slot-number qos account layer2 encapsulation {arpa | dot1q | length} global configuration command. When enabled, the feature is enabled on all ports of the line card in both ingress and egress directions. Layer 3 accounting is the default. The no form of the command enables the default. The show policy-map interface and show interface rate commands display the additional Layer 2 overhead length.
For the Cisco 12000 Series 4-Port Gigabit Ethernet ISE Line Card, the Layer 2 encapsulation overhead options to specify are as follows:
The specified byte length in the CLI is used only in the egress (Tx) direction. Output shaping or policing must be configured on an interface. The bit rate transmitted from the line card is determined by adding the Layer 3 length of the packet to the length defined in the CLI.
Incoming packets are shaped or policed based on the true Layer 2 length of the packets. For example, if the user-specified length is 14 bytes, and all packets egressing from any port are ARPA main interface packets, then the results are accurate. If some egress packets have VLAN encapsulations and some are non-VLAN (main interface) packets, then the results cannot be completely accurate because the encapsulation overheads are different. On the input side, Layer 2 encapsulation overhead is 14 bytes for ARPA main interface packets and 18 bytes for 802.1Q packets, regardless of the user-specified length.
Restrictions
•
•
SUMMARY STEPS
1.
2.
3.
4.
DETAILED STEPS
Additional References
The following sections provide references related to QoS: L2 Overhead Specification for Shaping and Policing Parameters for Ethernet.
Related Documents
Quality of service (QoS) commands: complete command syntax, command modes, command history, defaults, usage guidelines, and examples
Cisco IOS Quality of Service Solutions Command Reference, Release 12.3 T
Modular QoS Command-Line Interface (CLI) (MQC)
Information about attaching policy maps to interfaces
Traffic policing
Technical Assistance
Command Reference
This section documents modified commands. All other commands used with this feature are documented in the Cisco IOS Release 12.0 command reference publications.
hw-module slot qos account layer2 encapsulation
To enable Layer 2 accounting for QoS, use the command in global configuration mode. To disable, use the no form of this command.
hw-module slot slot-number qos account layer2 encapsulation {arpa | dot1q | length}
no hw-module slot slot-number qos account layer2 encapsulation {arpa | dot1q | length}
Syntax Description
Defaults
No Layer 2 encapsulation accounting is the default.
Command Modes
Global configuration
Command History
Usage Guidelines
The no version of the command enables the default method of calculating the bit rate of traffic over an interface based on Layer 3 packet lengths.
The length parameter specifies Layer 2 overhead for output traffic only. The packets transmitted from the line card are shaped or policed by adding the user-specified length to the Layer 3 length of the output packets. The incoming packets are shaped or policed according to the actual Layer 2 lengths of the encapsulations, regardless of the user-specified length.
For Any Transport over ATM (AToM), the user specified byte length on the egress of the disposition router is still added to the length of the packet though there is no Layer 2 transport encapsulation on the packet.
The following example specifies that 16 bytes of Layer 2 encapsulation overhead are added for each Layer 3 packet egressing from the linecard:
Router(config)# hw-module slot 1 qos account layer2 encapsulation 16Related Commands
Copyright © 2004 Cisco Systems, Inc. All rights reserved.
