Classification Based On Class Maps And Policy Maps - Cisco Catalyst 4500 Series Software Configuration Manual

Chapter 44 Configuring Quality of Service
or IP extended ACLs or MAC ACLs. For more information, see the
and Policy Maps" section on page
If the class map is configured to match all the match criteria, then a packet must satisfy all the match
statements in the class map before the QoS action is taken. The QoS action for the packet is not taken if
the packet does not match even one match criterion in the class map.
If the class map is configured to match at least one match criterion, then a packet must satisfy at least
one of the match statements in the class map before the QoS action is taken. The QoS action for the
packet is not taken if the packet does not match any match criteria in the class map.
When you use the IP standard and IP extended ACLs, the permit and deny ACEs in the ACL have a
Note
slightly different meaning in the QoS context.
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•
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Note When creating an access list, remember 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.
After a traffic class has been defined with the class map, you can create a policy that defines the QoS
actions for a traffic class. 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.
When a class-map is created with the match-all keyword, you cannot include both IP and MAC ACLs
as match criteria.

Classification Based on Class Maps and Policy Maps

A class map is a mechanism that you use to isolate and name a specific traffic flow (or class) from all
other traffic. The class map defines the criterion 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, IP precedence, or L2 CoS 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 can specify the QoS actions via a policy map.
A policy map specifies the QoS actions for the traffic classes. Actions can include setting a specific CoS,
DSCP, or IP precedence value; policing the traffic to a specified rate; specifying the traffic bandwidth
limitations; shaping the traffic to a specified rate. Before a policy map can be effective, you must attach
it to an interface.
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 criteria for the traffic by using the match class-map configuration command.
If a packet encounters (and satisfies) an ACE with a "permit," then the packet "matches" the match
criterion in the QoS classification.
If a packet encounters (and satisfies) an ACE with a "deny," then the packet "does not match" the
match criterion in the QoS classification.
If no match with a permit action is encountered and all the ACEs have been examined, then the
packet "does not match" the criterion in the QoS classification.
Catalyst 4500 Series Switch, Cisco IOS Software Configuration Guide - Cisco IOS XE 3.9.xE and IOS 15.2(5)Ex
44-7.
Overview of QoS
"Classification Based on Class Maps
44-7