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8.6 Aggregates and Microflow’s

Aggregates and Microflow’s are terms used to define the scope of policing that the PFC performs. A Microflow

defines the policing of a single flow. The flow mask installed in the system defines how the Microflow Policer views a

flow. Typically the default flow mask for Microflow policing is defined as a session with a unique SA/DA MAC

address, SA/DA IP address and TCP/UDP port numbers or a source IP address. For each new flow that is initiated

through a port or a VLAN, the Microflow can be used to limit the amount of data sent or received for that flow by the

switch. In the Microflow definition, packets that exceed the prescribed rate limit can be either dropped or have their

DSCP value marked down. Microflow’s are applied using the police flow command that forms part of a policy map

class. Another important aspect of a Microflow policer is that it can only be applied to ingress traffic. It cannot be

applied to egress traffic.

Microflow policing can also be applied to bridged traffic that is traffic that is not Layer 3 switched. To enable the

switch to support Microflow policing on bridged traffic, this too must be enabled on the VLAN interface using the

following command:

Cat6500(config-if)# mls qos bridged

Microflow policing can also be used with the PFC3x to rate limit multiple microflows to the same limit based on

source or destination address with a single ACL (this is described further in the User Based Rate Limiting section).

Figure 33. Microflow Policer

Like a Microflow, an Aggregate can be used to rate limit traffic; however, the Aggregate rate applies to all traffic

inbound on a port or VLAN that matches a specified QoS ACL. The Aggregate Policer can be applied to either a

physical interface or a VLAN. If an Aggregate policer is applied to a single interface, then the Aggregate Policer will

count all matching traffic (that matches the classifying ACL) coming into the interface towards the policer. If the

Aggregate Policer is applied to a VLAN, then all of the matching traffic coming in any of the ports in that VLAN is

counted towards the stated Rate. An example of an aggregate could be a 20Mbps Aggregate policer applied to

VLAN 10. In VLAN 10 there are five ports (shown on the left hand side of the diagram below). This aggregate would

limit the total amount of traffic for those five ports to 10Mbps.