Cisco Catalyst 4500 Series Command Reference Manual page 684

set dscp
Usage Guidelines Once the DSCP bit is set, other quality of service (QoS) features can then operate on the bit settings.
DSCP and Precedence Values Are Mutually Exclusive
The set dscp command cannot be used with the set precedence command to mark the same packet. The
two values, DSCP and precedence, are mutually exclusive. A packet can have one value or the other, but
not both.
You can use this command to specify the "from-field" packet-marking category to be used for mapping
and setting the DSCP value. The "from-field" packet-marking categories are as follows:
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If you specify a "from-field" category but do not specify the table keyword and the applicable
table-map-name argument, the default action will be to copy the value associated with the "from-field"
category as the DSCP value. For instance, if you configure the set dscp cos command, the CoS value
will be copied and used as the DSCP value.
The CoS field is a three-bit field, and the DSCP field is a six-bit field. If you configure the set dscp cos
Note
command, only the three bits of the CoS field will be used.
If you configure the set dscp qos-group command, the QoS group value will be copied and used as the
DSCP value.
The valid value range for the DSCP is a number from 0 to 63. The valid value range for the QoS group
is a number from 0 to 63.
Set DSCP Values in IPv6 Environments
When this command is used in IPv6 environments, the default match occurs on both IP and IPv6 packets.
However, the actual packets set by this function are only those which meet the match criteria of the
class-map containing this function.
Set DSCP Values for IPv6 Packets Only
To set DSCP values for IPv6 values only, the match protocol ipv6 command must also be used. Without
that command, the DSCP match defaults to match both IPv4 and IPv6 packets.
Set DSCP Values for IPv4 Packets Only
To set DSCP values for IPv4 packets only, use the ip keyword in the match command for classification.
Without the ip keyword, the match occurs on both IPv4 and IPv6 packets.
Examples
Packet-marking Values and Table Map
In the following example, the policy map called policy1 is created to use the packet-marking values
defined in a table map called table-map1. The table map was created earlier with the table-map (value
mapping) command. For more information about the table-map (value mapping) command, see the
table-map (value mapping) command page.
Catalyst 4500 Series Switch Cisco IOS Command Reference—Release IOS XE 3.4.0SG and IOS 15.1(2)SG)
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Class of service (CoS)
QoS group
Precedence
Differentiated services code point (DSCP)
Chapter 2 Cisco IOS Commands for the Catalyst 4500 Series Switches
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