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Catalyst 3550 Multilayer Switch Software Configuration Guide
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Chapter20 Co nf iguring QoS
Configuring QoS
Configuration Guidelines
Before beginning the QoS configuration, you should be aware of this information:
•If you have EtherChannel ports configured on your switch, you mu st configure QoS classification,
policing, mapping, and queueing on the individual phys ica l po rts t h at c ompr ise th e Eth erC hanne l.
You must decide whether the QoS configuration should match on all ports in the EtherChannel.
•You configure QoS only on physical ports; there is no support for it on the VLAN or switch virtual
interface level.
•It is not possible to match IP fragments against configured IP extended ACLs to enforce QoS. IP
fragments are sent as best-effort. IP fragments are denoted by fields in the IP header.
•You can match IP options against configured IP extended ACLs to enforce QoS. These packets are
sent to the CPU and processed by software. IP options are denoted by fields in the IP header.
•Control traffic (such as spanning-tree bridge protocol data uni ts [B PDUs ] a nd ro uting upd ate
packets) received by the switch are subject to all ingress QoS processing.
•You must disable the IEEE 802.3X flowcontrol on all ports before enabling QoS on the switch. To
disable it, use the flowcontrol rec e i ve of f and fl owcontrol send off interface configuration
commands.
•Only one ACL per class map and only one match class-map configuration command pe r cl ass map
are supported. The ACL can have multiple access control entries, which are commands that match
fields against the contents of the packet.
•Use only the match ip dscp dscp-list class-map configuration command in a policy map that is
attached to an egress interface.
•Policy maps with ACL classification in the egress direction are not su pported and cannot be attached
to an interface by using the service-policy output policy-map-name interface configuration
command. Policy maps containing set or trust policy-map class configuration commands cannot be
attached to an egress interface; instead, you can use the police policy-map class configuration
command to mark down (reduce) the DSCP value at the egress in terf ace.
•You can create an aggregate policer that is shar ed by m ult ipl e tr affic classes within the same policy
map. However, you cannot use the aggregate policer across different policy maps or interfaces.