Set Ip Dscp Command History; Usage Guidelines For The Set Ip Dscp Command; Class Of Service Marking - Cisco 10000 Series Configuration Manual
Quality of service configuration guide
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Class of Service Marking
set ip dscp Command History
Cisco IOS Release
Release 12.0(17)SL
Release 12.2(16)BX
Release 12.2(28)SB
Release 12.2(31)SB2
Release 12.2(33)SB
Usage Guidelines for the set ip dscp Command
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Class of Service Marking
Class of service (CoS) marking enables the Cisco 10000 series router to interoperate with switches to
deliver end-to-end QoS. The IEEE 802.1p standard enables the router to:
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For Layer 2 devices, you can assign priority-indexed IEEE 802.1p CoS values to Ethernet frames.
Layer 2 IEEE 802.1Q frame headers have a 2-byte Tag Control Information field in the 802.1p portion
of the header. The three most-significant bits of this field (the User Priority bits) make up the Layer 2
CoS field. This 3-bit field allows you to mark eight classes of service (0 through 7) on Layer 2 Ethernet
frames. Other QoS tools can then use the CoS marking to classify traffic. For IEEE 802.1Q, the User
Priority bits are set to zero (0) in the Ethernet header.
Figure 7-2
Cisco 10000 Series Router Quality of Service Configuration Guide
7-10
Description
This command was introduced on the PRE1.
This command was introduced on the PRE2.
This command was integrated in Cisco IOS Release 12.2(28)SB for the
PRE2.
This command was introduced on the PRE3 to allow you to mark the IP
DSCP bits of traffic on the L2TP access concentrator (LAC).
This command was introduced on the PRE4.
After the DSCP bit is set, other quality of service (QoS) features can then operate on the bit settings.
You cannot use the set ip dscp command with the set ip precedence command to mark the same
packet. DSCP and precedence values are mutually exclusive. A packet can have one value or the
other, but not both.
The network can give priority (or some type of expedited handling) to marked traffic. Typically, you
set the precedence value at the edge of the network (or administrative domain); data is then queued
according to the precedence. Weighted fair queuing (WFQ) can speed up handling for
high-precedence traffic at congestion points. Weighted random early detection (WRED) can ensure
that high-precedence traffic has lower loss rates than other traffic during times of congestion.
In Cisco IOS Release 12.3(7)XI, the router accepts the set dscp command without specifying the
ip keyword. However, you must specify the set ip dscp command to set the DSCP value in a packet
header. The ip keyword is required.
Classify inbound Ethernet packets based on the value in the CoS field
Set the value in the CoS field of outbound packets
shows the PRI field containing the 3-bit User Priority field.
Chapter 7
Marking Traffic
OL-7433-09
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