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Catalyst2950 and Catalyst2955 Switch Software Configuration Guide
78-11380-10
Chapter30 Configuring QoS Configuring Standard QoS
Note In software releases earlier than Cisco IOS Release12.1(11)EA1, the switch uses the CoS value of
incoming packets without modifying the DSCP value. You can configure this by enabling pass-through
mode on the port. For more information, see the “Enabling Pass-Through Mode” section on page30 -25.
Configuration Guidelines
Note These guidelines are applicable only if your switch is running the EI.
Before beginning the QoS configuration, you should be aware of this information:
•You must disable the IEEE 802.3x flowcontrol on all ports before enabling QoS on the switch. To
disable it, use the flowcontrol rece ive of f and flowcontrol send off interface configuration
commands.
•If you have EtherChannel ports configured on your switch, you must configure QoS classification,
policing, mapping, and queueing on the individual physical por ts t ha t co mpri se t he E t herCh an nel.
You must decide whether the QoS configuration should match on all ports in the EtherChannel .
•It is not possible to match IP fragments against configured IP extended ACLs to enforce QoS. IP
fragments are sent as best-effort traffic. IP fragments are denoted by fields in the IP header.
•All ingress QoS processing actions apply to control traffic (such as spanning-tree bridge protocol
data units [BPDUs] and routing update packets) that the switch receives.
•Only an ACL that is created for physical interfaces can be attached to a class map.
•Only one ACL per class map and only one match command per class map are supported. The ACL
can have multiple access control entries, which are commands th at match fields against the contents
of the packet.
•Policy maps with ACL classification in the egress direction are not supported and cannot be attached
to an interface by using the service-policy input policy-map-name interface configuration
command.
•In a policy map, the class named class-default is not supported. The switch does not filter traffic
based on the policy map defined by the class class-default policy-map configuration command.
•For more information about guidelines for configuring ACLs, see the “Classification Based on QoS
ACLs” section on page 30-5.
•For information about applying ACLs to physical interfaces, see the “Guidelines for Applying ACLs
to Physical Interfaces” section on page29-5.
•If a policy map with a system-defined mask and a security ACL with a user-defined mask are
configured on an interface, the switch might ignore the acti on s sp eci fied by th e policy m ap a nd
perform only the actions specified by the ACL. For information about masks, se e t he
“Understanding Access Control Parameters” section on page29-4 .
•If a policy map with a user-defined mask and a security ACL with a user-defined mask are
configured on an interface, the switch takes one of the actions a s desc ribe d in Ta ble 30 -5. For
information about masks, see the “Understanding Access Control Parameters” section on page 29-4.