3550 QOS

knight_net

Classification occurs only on a physical interface basis. No support exists for classifying packets at the VLAN or the switched virtual interface level.
We strongly recommend that you disable the IEEE 802.3x flowcontrol on all ports before enabling QoS on the switch. To disable it, use the flowcontrol receive off and flowcontrol send off interface configuration commands.
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 that match fields against the contents of the packet.
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Policy maps with ACL classification in the egress direction are not supported 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 interface
If you want to use set command in the policy map and are using the Layer 3 switch image, you must enable IP routing (disabled by default) and configure an IP default route to send traffic to the next-hop device that is capable of forwarding.
By default, QoS is disabled on the switch, which means that the switch offers best-effort service to each packet regardless of the packet contents or size. All packets pass through the switch without modification; all CoS values map to egress queue 1 with both tail-drop thresholds set to 100 percent of the total queue size.
Beginning in privileged EXEC mode, follow these steps to enable QoS:

Command
Purpose
Step 1
configure terminal
Enter global configuration mode.
Step 2
interface range gi0/1 -12
Enter interface configuration mode, and execute a command on multiple interfaces.
Step 3
flowcontrol receive off
flowcontrol send off
Disable flowcontrol on all interfaces.
Step 4
exit
Return to global configuration mode.
Step 5
mls qos
Enable QoS globally.
Step 6
end
Return to privileged EXEC mode.
Step 7
show mls qos
Verify your entries.
Step 8
copy running-config startup-config
(Optional) Save your entries in the configuration file.


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