Egress Classification Based On Traffic Classes And Traffic Policies - Cisco Catalyst 3750 Software Configuration Manual

Chapter 26 Configuring QoS

Egress Classification Based on Traffic Classes and Traffic Policies

Egress classification is the process of distinguishing one kind of traffic from another by examining the
fields in the packet, processing the match commands, and creating the egress queues before the switch
sends the packet out the ES port.
You use the class map to define a specific traffic flow (or class) and to isolate it from all other traffic.
The class map defines the criteria used to match against a specific traffic flow to further classify it. At
the class level, the criteria can include matching CoS, DSCP, IP precedence, or MPLS EXP bits in the
header. At the VLAN level, the criteria can include matching a packet based on the inner and the outer
VLAN IDs. If you have more than one type of traffic that you want to classify, you can create another
class map and use a different name.
You create a class map by using the class-map global configuration command. When you enter the
class-map command, the switch enters the class-map configuration mode. In this mode, you define the
match criterion for the traffic by using the match class-map configuration command. Outbound packets
are checked against the match criteria configured for a class map. If a packet matches the specified
criteria, the packet is considered a member of the class, the switch creates a queue for it, and the packet
is forwarded according to the QoS specifications set in the traffic policy. If a packet fails to meet any of
the matching criteria, it is classified as a member of the default traffic class if one is configured.
You use the policy map to create the traffic policy, to specify the traffic class to act on, and to configure
the QoS features associated with the traffic class. Actions can include trusting the received CoS, DSCP,
or IP precedence bits in the traffic class; setting specific CoS, DSCP, IP precedence, or MPLS EXP bits
in the traffic class; or specifying the traffic bandwidth limitations and the action to take when the traffic
is out of profile.
You create and name a policy map by using the policy-map global configuration command. When you
enter this command, the switch enters the policy-map configuration mode. In this mode, you use the
class policy-map configuration command to name the traffic class associated with the traffic policy. If
you specify class-default as the class name in the class policy-map configuration command, packets that
fail to meet any of the matching criteria are classified as members of the default traffic class. You can
manipulate this class (for example, police it and mark it) just like any traffic class, but you cannot delete
it.
Within a policy-map, the class-default designates all traffic that is not explicitly matched within the
policy-map but does match the policy map of the parent policy. If no parent policy is configured, the
parent policy represents the physical port. In the physical-level policy-map, class-default is the only
class that can be configured.
After you name the traffic class with the class command, the switch enters policy-map class
configuration mode, and you can specify the actions to take on this traffic class.
You attach an egress policy-map to an ES port by using the service-policy output interface configuration
command. The egress policy-map can include the bandwidth, police cir, police cir percent, priority,
queue-limit, random-detect, shape, or set policy-map class configuration commands. If the policy map
contains the class-default class, you can configure settings only through the police cir, police cir
percent, and shape commands.
For more information, see the
and Scheduling of Hierarchical Queues" section on page
78-15870-01
Switch(config)# interface gigabitethernet1/1/1
Switch(config-if)# service-policy output my-physical-policy
"Egress Policing and Marking" section on page 26-24
26-26.
Catalyst 3750 Metro Switch Software Configuration Guide
Understanding Hierarchical QoS
and the "Queueing
26-23