Cisco 3560G 48TS Software Configuration Guide - Page 531

Policing and Marking Flowchart, policy-map class configuration command or

Page 531 highlights

Chapter 28 Configuring QoS Understanding QoS 78-16156-01 Policing uses a token-bucket algorithm. As each frame is received by the switch, a token is added to the bucket. The bucket has a hole in it and leaks at a rate that you specify as the average traffic rate in bits per second. Each time a token is added to the bucket, the switch verifies that there is enough room in the bucket. If there is not enough room, the packet is marked as nonconforming, and the specified policer action is taken (dropped or marked down). How quickly the bucket fills is a function of the bucket depth (burst-byte), the rate at which the tokens are removed (rate-bps), and the duration of the burst above the average rate. The size of the bucket imposes an upper limit on the burst length and limits the number of frames that can be transmitted back-to-back. If the burst is short, the bucket does not overflow, and no action is taken against the traffic flow. However, if a burst is long and at a higher rate, the bucket overflows, and the policing actions are taken against the frames in that burst. You configure the bucket depth (the maximum burst that is tolerated before the bucket overflows) by using the burst-byte option of the police policy-map class configuration command or the mls qos aggregate-policer global configuration command. You configure how fast (the average rate) that the tokens are removed from the bucket by using the rate-bps option of the police policy-map class configuration command or the mls qos aggregate-policer global configuration command. After you configure the policy map and policing actions, attach the policy to an ingress port by using the service-policy interface configuration command. For configuration information, see the "Classifying, Policing, and Marking Traffic by Using Policy Maps" section on page 28-42 and the "Classifying, Policing, and Marking Traffic by Using Aggregate Policers" section on page 28-45. Figure 28-4 Policing and Marking Flowchart Start Get the clasification result for the packet. Is a policer configured No for this packet? Yes Check if the packet is in No profile by querying the policer. Yes Pass through Check out-of-profile action configured for this policer. Mark Drop Drop packet. Modify DSCP according to the policed-DSCP map. Generate a new QoS label. Done 86835 Catalyst 3560 Switch Software Configuration Guide 28-9

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28-9
Catalyst 3560 Switch Software Configuration Guide
78-16156-01
Chapter 28
Configuring QoS
Understanding QoS
Policing uses a token-bucket algorithm. As each frame is received by the switch, a token is added to the
bucket. The bucket has a hole in it and leaks at a rate that you specify as the average traffic rate in bits
per second. Each time a token is added to the bucket, the switch verifies that there is enough room in the
bucket. If there is not enough room, the packet is marked as nonconforming, and the specified policer
action is taken (dropped or marked down).
How quickly the bucket fills is a function of the bucket depth (burst-byte), the rate at which the tokens
are removed (rate-bps), and the duration of the burst above the average rate. The size of the bucket
imposes an upper limit on the burst length and limits the number of frames that can be transmitted
back-to-back. If the burst is short, the bucket does not overflow, and no action is taken against the traffic
flow. However, if a burst is long and at a higher rate, the bucket overflows, and the policing actions are
taken against the frames in that burst.
You configure the bucket depth (the maximum burst that is tolerated before the bucket overflows) by
using the
burst-byte
option of the
police
policy-map class configuration command or the
mls qos
aggregate-policer
global configuration command. You configure how fast (the average rate) that the
tokens are removed from the bucket by using the
rate-bps
option of the
police
policy-map class
configuration command or the
mls qos aggregate-policer
global configuration command.
After you configure the policy map and policing actions, attach the policy to an ingress port by using the
service-policy
interface configuration command. For configuration information, see the
“Classifying,
Policing, and Marking Traffic by Using Policy Maps” section on page 28-42
and the
“Classifying,
Policing, and Marking Traffic by Using Aggregate Policers” section on page 28-45
.
Figure 28-4
Policing and Marking Flowchart
86835
Yes
Yes
No
No
Pass
through
Drop
Mark
Get the clasification
result for the packet.
Is a policer configured
for this packet?
Check if the packet is in
profile by querying the policer.
Check out-of-profile action
configured for this policer.
Drop packet.
Modify DSCP according to the
policed-DSCP map. Generate
a new QoS label.
Start
Done