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Catalyst 2950 Desktop Switch Software Configuration Guide
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Chapt er 26 Conf i gurin g QoS
Configuring QoS

Configuration Guidelines

Note Th ese guide lines are applicab le only if you r switch is ru nning the E I.
Before beginni ng the QoS configu ration, yo u should be aware of this informat ion:
•If you have EtherCh an nel ports c on figured o n your sw it ch, yo u m ust co nfigure Q oS cl ass ification,
polici ng, m ap ping, an d qu eu ei ng o n t he in dividual p hysic al p or ts t hat co mpri se t he E t herCh an nel.
You must deci de whet her t he Q oS configur ation sho ul d ma tch on al l po rts i n the Et herCh an nel.
•It is not pos sible to mat ch IP fragm ents against configur ed IP extended ACLs to en force Qo S. IP
fragments are sent as best-effort traffic. IP fragments are denoted by fields in the IP header.
•All ingress Q oS processing ac tions apply t o cont rol traffic (suc h as spanning-t ree bridg e protoco l
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 ma p and only one match command per class ma p are supported. The ACL
can have multiple access control entries, which are commands that 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- ma p-n ame interface configuration
command.
•In a po l icy ma p, t he c lass na med class-default is not supported. The switch does not filter traffic
based on the policy map defined by the class class-default pol icy-map co nfiguration command.
•For more informati on abo ut guidelines f or conf ig uring ACLs, see the “Classif ication Based on QoS
ACLs” section on page 26-5.
•For information about applying A CLs to physical interfaces, see the “Guidelines for Applying ACLs
to Physical Interfaces” section on page 25-6.
Note Do not co nfigure QoS whe n I EEE 80 2.3 X fl owcontr ol is co nfigur ed on t he s wit ch. Be for e c onfiguring
QoS on an interface, make sure to disable flowcontrol on the switch.

Configuring Classification Using Port Trust States

This se ction de scri bes how to cla ssify inc omi ng t raffic by using por t tru st st ates :
•Configuring the Trust State on Ports within the QoS Domain, page 26-11
•Configuring the CoS Value for an Interface, page 26-13
•Configuring Trusted Bou nda ry, pag e 26- 13
•Enab ling Pa ss-Thr ough M ode, p age 26- 15