QoS group

■ Multiprotocol Label Switching (MPLS) experimental bits

■ IEEE 802.1Q or Inter-Switch Link (ISL) CoS/priority bits

■ Frame Relay discard eligible (DE) bit

You can combine class-based marking with other mechanisms available in the MQC.

This topic describes the Cisco IOS commands that are required to configure class-based marking.

When configuring class-based marking, you must complete these three configuration steps: Step 4 Create a class map Step 5 Create a policy map

Step 6 Attach the policy map to an interface by using the service-policy Cisco IOS command.

class-map {match any | match all} class-map-name

Syntax Description


Descri ption


Name of the class for the class map. The class name is used for both the class map and to configure policy for the class in the policy map.

match-any | match-all

Determines how packets are evaluated when multiple match criteria exist. Packets must either meet all of the match criteria (match-all) or one of the match criteria (match-any) to be considered a member of the class.

policy-map policy-map-name Syntax Description




Name of the policy map

service-policy {input | output} policy-map-name Syntax Description




Specifies the name of the predefined policy map to be used as a QoS policy. The name can be a maximum of 40 alphanumeric characters.

Connecting the IP Phone

802.1Q trunking between the switch and IP Phone for multiple VLAN support (separation of voice and data traffic) is preferred.

The 802.1Q header contains the VLAN information and the CoS 3-bit field, which determines the priority of the packet.

For most Cisco IP Phone configurations, traffic sent from the IP Phone to the switch is trusted to ensure that voice traffic is properly prioritized over other types of traffic in the network.

The trusted boundary feature uses CDP to detect an IP Phone and otherwise disables the trusted setting on the switch port to prevent misuse of a high-priority queue.

In the figure, two class maps have been configured, Well-known-services and Unknown-services. The match criteria is specified in access-list 100.

The policy map, set-DSCP, has been created to associate with the class-maps Well-known-services and Unknown-services.

For packets allowed by class map Well-known-services, the IP DSCP value will be set to AF21. The matching class map Unknown-services will have the IP DSCP value set to 0.

The policy map is attached to E0/0 for incoming packets by the service-policy command.

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This topic describes the Cisco IOS commands that are required to mark IP packets using CoS with class-based marking.

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