Cisco Systems 3750E manual Policing Guidelines, General QoS Guidelines, 36-36

Chapter 36 Configuring QoS

Configuring Standard QoS

•Follow these guidelines when configuring policy maps on physical ports or SVIs:

–You cannot apply the same policy map to a physical port and to an SVI.

–If VLAN-based QoS is configured on a physical port, the switch removes all the port-based policy maps on the port. The traffic on this physical port is now affected by the policy map attached to the SVI to which the physical port belongs.

–In a hierarchical policy map attached to an SVI, you can only configure an individual policer at the interface level on a physical port to specify the bandwidth limits for the traffic on the port. The ingress port must be configured as a trunk or as a static-access port. You cannot configure policers at the VLAN level of the hierarchical policy map.

–The switch does not support aggregate policers in hierarchical policy maps.

–After the hierarchical policy map is attached to an SVI, the interface-level policy map cannot be modified or removed from the hierarchical policy map. A new interface-level policy map also cannot be added to the hierarchical policy map. If you want these changes to occur, the hierarchical policy map must first be removed from the SVI. You also cannot add or remove a class map specified in the hierarchical policy map.

Policing Guidelines

These are the 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

These are 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.

	Catalyst 3750-E and 3560-E Switch Software Configuration Guide
36-36	OL-9775-02