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Catalyst 3750-X and 3560-X Switch Software Configuration Guide
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Chapter 39 Configuring QoS
Configuring Standard QoS
• QoS policies that include IPv6-specific classification (such as an IPv6 ACL or the match protocol
ipv6 command) are supported on Catalyst 3750-X and Catalyst 3750-E interfaces and on any SVI
when a Catalyst 3750-X or Catalyst 3750-E switch is part of the stack.
• QoS policies that include common IPv4 and IPv6 classifications are supported on all
Catalyst 3750-X and Catalyst 3750-E interfaces in the stack. Only IPv4 classification is supported
on other switches in the stack.

Policing Guidelines

• The port ASIC device, which controls more than one physical port, supports 256 policers
(255 user-configurable e policers plus 1 policer reserved for system internal use). The maximum
number of user-configurable policers supported per port is 63. For example, you could configure 32
policers on a Gigabit Ethernet port and 7 policers on a 10-Gigabit Ethernet port, or you could
configure 64 policers on a Gigabit Ethernet port and 4 policers on a 10-Gigabit Ethernet port.
Policers are allocated on demand by the software and are constrained by the hardware and ASIC
boundaries. You cannot reserve policers per port; there is no guarantee that a port will be assigned
to any policer.
• Only one policer is applied to a packet on an ingress port. Only the average rate and committed burst
parameters are configurable.
• You can create an aggregate policer that is shared by multiple traffic classes within the same
nonhierarchical policy map. However, you cannot use the aggregate policer across different policy
maps.
• On a port configured for QoS, all traffic received through the port is classified, policed, and marked
according to the 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 queueing on the individual physical ports that comprise the EtherChannel.
You must decide whether the QoS configuration should match on all ports in the EtherChannel.

General QoS Guidelines

• 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.
• A switch that is running the IP services feature set supports QoS DSCP and IP precedence matching
in policy-based routing (PBR) route maps with these limitations:
–
You cannot apply QoS DSCP mutation maps and PBR route maps to the same interface.
–
You cannot configure DSCP transparency and PBR DSCP route maps on the same switch.
Enabling QoS Globally
By default, QoS is disabled on the switch. To enable IPv6 QoS on the switch, you must first configure a
dual-ipv4-and ipv6 SDM template and reload the switch. This template enables both IPv4 and IPv6 QoS
configuration.