Cisco Catalyst QoS: Quality of Service in Campus Networks

300 Chapter 8: QoS Support on the Catalyst 6500

Policing

Policing is another feature available on the Catalyst 6500. Policing enables the adminis-

trator to control bandwidth utilization for certain applications. This guarantees the

necessary bandwidth for voice and video and other mission-critical applications. Policing

is performed in hardware on the PFC without impacting switch performance. Policing

cannot occur on the 6500 platform without a PFC and is currently only supported for

ingress traffic. The PFC version within the platform determines the extent of the policing

functionality. The Catalyst 6500 offers both single-rate and two-rate policing.

The purpose of this section is to explain policing operation, as it pertains to the Catalyst

6500. It includes a discussion of microflow and aggregate policers, single-rate policing on

the PFC1 and PFC2, and two-rate policing on the PFC2. Finally, the section includes

numerous configuration examples and various show commands used to verify operation.

Microflow and Aggregate Policers

Two types of policers are available on the Catalyst 6500: microflow and aggregate policers.

Microflow policers limit the bandwidth consumed by individual flows on a port-by-port or

interface basis. A flow is very specific and can be defined using Layer 3 source and desti-

nation addresses, Layer 4 protocol type, and Layer 4 source and destination port numbers.

The bandwidth limitation is applied to each flow matching the criteria defined in the ACLs

separately. The Catalyst 6500 can support up to 63 microflow policers.

Aggregate policers limit an aggregate of individual flows across multiple ports or inter-

faces, or on a single port or interface, to one specified rate. The shared aggregate policer

polices all traffic to a configured rate for all ports to which the policer is applied. On the

other hand, the interface aggregate policer polices all flows for each individual interface.

Up to 1023 aggregate policers can be defined on the Catalyst 6500.

Consider the following example. Assume there is a microflow policer defined limiting the

bandwidth consumption for certain IPTV streams to 1.5 Mbps. After the policer has been

defined, it is applied to the appropriate interfaces, in this case ports 5/1 and 5/3. In this case,

d1 : d2 0 1 2 3 4 5 6 7 8 9

-------------------------------------

0 : 00 01 02 03 04 05 06 07 08 09

1 : 10 11 12 13 14 15 16 17 18 19

2 : 20 21 22 23 00 25 26 27 28 29

3 : 30 31 32 33 34 35 36 37 38 39

4 : 40 41 42 43 44 45 46 47 48 49

5 : 50 51 52 53 54 55 56 57 58 59

6 : 60 61 62 63

(text omitted)

Example 8-30 Modifying the Policed DSCP Mark-Down Table in Native Mode (Continued)

Policing 301

although one microflow policer has been defined and applied to the two separate ports, all

IPTV traffic matching the configured criteria is limited to 1.5 Mbps per flow. Therefore, if

one flow exists on port 5/1 and two flows exist on port 5/3, each flow is limited to 1.5 Mbps,

for a combined total of 4.5 Mbps. Aggregate policers differ slightly. Consider the same

situation, but now the configured policer is an aggregate policer. In this case, the combined

inbound flows for port 5/1 and port 5/3 are considered and allocated a total of 1.5 Mbps.

Any traffic exceeding this rate is classified as nonconforming and subsequently policed.

Figure 8-8 Microflow Versus Aggregate Policer

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Policer

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Policer

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Policer

Microflow Policing

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Aggregate Policing

Policer