Classification Based On Class Maps And Policy Maps - Cisco Catalyst 2960 series Configuration Manual

• If a match with a permit action is encountered (first-match principle), the specified QoS-related action
is taken.
• If a match with a deny action is encountered, the ACL being processed is skipped, and the next ACL is
processed.
• If no match with a permit action is encountered and all the ACEs have been examined, no QoS processing
occurs on the packet, and the switch offers best-effort service to the packet.
• If multiple ACLs are configured on a port, the lookup stops after the packet matches the first ACL with
a permit action, and QoS processing begins.
Note
After a traffic class has been defined with the ACL, you can attach a policy to it. A policy might contain
multiple classes with actions specified for each one of them. A policy might include commands to classify
the class as a particular aggregate (for example, assign a DSCP) or rate-limit the class. This policy is then
attached to a particular port on which it becomes effective.
You implement IP ACLs to classify IP traffic by using the access-list global configuration command; you
implement Layer 2 MAC ACLs to classify non-IP traffic by using the mac access-list extended global
configuration command.
Related Topics
Creating an IP Standard ACL for IPv4 Traffic, on page 584
Creating an IP Extended ACL for IPv4 Traffic, on page 586
Creating an IPv6 ACL for IPv6 Traffic, on page 588
Creating a Layer 2 MAC ACL for Non-IP Traffic, on page 590

Classification Based on Class Maps and Policy Maps

To use policy maps, the switch must be running the LAN Base image.
A class map is a mechanism that you use to name 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. The criteria can include matching the access group defined by the ACL or matching a specific list of DSCP
or IP precedence values. 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. After a packet is matched against the class-map criteria, you
further classify it through the use of a policy map.
A policy map specifies which traffic class to act on. Actions can include trusting the CoS, DSCP, or IP
precedence values in the traffic class; setting a specific DSCP or IP precedence value in the traffic class; or
specifying the traffic bandwidth limitations and the action to take when the traffic is out of profile. Before a
policy map can be effective, you must attach it to a port.
You create a class map by using the class-map global configuration command or the class policy-map
configuration command. You should use the class-map command when the map is shared among many ports.
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.
When creating an access list, note that by default the end of the access list contains an
implicit deny statement for everything if it did not find a match before reaching the end.
Consolidated Platform Configuration Guide, Cisco IOS Release 15.2(4)E (Catalyst 2960-X Switches)
Information About QoS
549