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Cisco ME 3400 EthernetAccess Switch SoftwareConfiguration Guide
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Chapter30 Configuring QoS Configuring QoS
Default QoS Configuration
There are no policy maps, class maps, table maps, or poli cer s c onfigure d. A t th e egre ss port , al l t raffic
goes through a single default queue that is given the full operational port bandwidth. The default size of
the default queue is 48 (256-byte) packets.
The packets are not modified (the CoS, DSCP, and IP precedence values in the packet are not changed).
Traffic is switched in pass-through mode without any rewrites and classified as best effort withou t any
policing.
QoS Configuration Guidelines
Before beginning the QoS configuration, you should be aware of these cond ition s :
•You can configure QoS only on physical ports.
•On a port configured for QoS, all traffic received through the port is classified, pol iced, and marked
according to the input policy map attached to the port. On a trunk port configured for QoS, traffic
in all VLANs received through the port is classified, policed, and marked according to the policy
map attached to the port.
•If you have EtherChannel ports configured on your switch, you must configure QoS classification,
policing, mapping, and queuing on the individual physical ports t hat com prise th e Ethe rC ha nnel .
You must decide whether the QoS configuration should match on all ports in the EtherChannel .
•Control traffic (such as spanning-tree bridge protocol data units [BPDUs] and routing update
packets) received by the switch are subject to all ingress QoS processing.
•You are likely to lose data when you change queue settings; therefore, try to make changes when traffic
is at a minimum.
See the configuration sections for specific QoS features for more conf iguration guide lines related to e ach
feature.
Using ACLs to Classify Traffic
You can classify IP traffic by using IP standard or IP extended ACLs. You can classify IP and non-IP
traffic by using Layer 2 MAC ACLs. For more information about configuring ACLs, see Chapter 28,
“Configuring Network Security with ACLs.”
Follow these guidelines when configuring QoS ACLs:
•You cannot 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.
•The switch supports only one access group per class in an input policy map.
•You cannot configure match-access group in an output policy map.
These sections describe how to create QoS ACLs:
•“Creating IP Standard ACLs” section on page 30-28
•“Creating IP Extended ACLs” section on page 30-29
•“Creating Layer 2 MAC ACLs” section on page 30-30