Cisco Catalyst 2960 Series, Configuration Manual

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policy map to the interfaces. If you do not first remove the policy map from all interfaces, high CPU
usage can occur, which, in turn, can cause the console to pause for a very long time.
General QoS Guidelines
These are the general QoS guidelines:
• You configure QoS only on physical ports; there is no support for it at the VLAN level.
• 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.
• The switch supports homogeneous stacking and mixed stacking. Mixed stacking is supported only with
the Catalyst 2960-S switches. A homogenous stack can have up to eight stack members, while a mixed
stack can have up to four stack members. All switches in a switch stack must be running the LAN Base
image.
Restrictions for QoS
The following are the restrictions for QoS:
• To use these features, the switch must be running the LAN Base image: stacking, DSCP, auto-QoS,
trusted boundary, policing, marking, mapping tables, and weighted tail drop.
• Ingress queueing is not supported.
• The switch supports 4 default egress queues, with the option to enable an additional 4 egress queues for
a total of 8. This option is only available on a standalone switch running the LAN Base image.
• We recommend that you do not enable 8 egress queues by using the mls qos srr-queue output queues
8
command, when running the following features in your configuration:
◦ Auto-QoS
◦ Auto SmartPort
◦ EnergyWise
Running these features with 8 egress queue enabled in a single configuration is not supported on the
switch.
• You can configure QoS only on physical ports. VLAN-based QoS is not supported. You configure the
QoS settings, such as classification, queueing, and scheduling, and apply the policy map to a port. When
configuring QoS on a physical port, you apply a nonhierarchical policy map to a port.
• If the switch is running the LAN Lite image you can:
◦ Configure ACLs, but you cannot attach them to physical interfaces. You can attach them to VLAN
interfaces to filter traffic to the CPU.
◦ Enable only cos trust at interface level.
◦ Enable SRR shaping and sharing at interface level.
Consolidated Platform Configuration Guide, Cisco IOS Release 15.2(4)E (Catalyst 2960-X Switches)
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Restrictions for QoS