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Catalyst 4500 Series Switch Cisco IOS Command Reference—Release IOS XE 3.4.0SG and IOS 15.1(2)SG)
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Chapter 2 Cisco IOS Commands for the Catalyst 4500 Series Switches
set precedence
You can use this command to specify the “from-field” packet-marking category to be used for mapping
and setting the precedence value. The “from-field” packet-marking categories are as follows:
• CoS
• QoS group
• DSCP
• Precedence
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 precedence value. For instance, if you configure the set precedence cos command, the
CoS value will be copied and used as the precedence value.
You can do the same for the QoS group-marking category. That is, you can configure the set precedence
qos-group command, and the QoS group value will be copied and used as the precedence value.
The valid value range for the precedence value is a number from 0 to 7. The valid value range for the
QoS group is a number from 0 to 63. Therefore, when configuring the set precedence qos-group
command the three least significant bits of qos-group are copied to precedence.
Precedence Values in IPv6 Environments
When this command is used in IPv6 environments it can set the value in both IPv4 and IPv6 packets.
However, the actual packets set by this function are only those that meet the match criteria of the
class-map containing this function.
Setting Precedence Values for IPv6 Packets Only
To set the precedence values for IPv6 packets only, the match protocol ipv6 command must also be used
in the class-map that classified packets for this action. Without the match protocol ipv6 command, the
class-map may classify both IPv6 and IPv4 packets, (depending on other match criteria) and the set
precedence command will act upon both types of packets.
Setting Precedence Values for IPv4 Packets Only
To set the precedence values for IPv4 packets only, use a command involving the ip keyword like the
match ip precedence or match ip dscp command or include the match protocol ip command along
with the others in the class map. Without the additional ip keyword, the class-map may match both IPv6
and IPv4 packets (depending on the other match criteria) and the set precedence or set dscp command
may act upon both types of packets.
Examples In the following example, the policy map named policy-cos is created to use the values defined in a table
map named table-map1. The table map named table-map1 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.
This example shows how the precedence value is set according to the CoS value defined in table-map1.
Switch# configure terminal
Switch(config)# policy-map policy-cos
Switch(config-pmap)# class class-default
Switch(config-pmap-c)# set precedence cos table table-map1
Switch(config-pmap-c)# end
Switch#
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