Cisco Catalyst 3550 series Software Configuration Manual page 595

Chapter 29 Configuring QoS
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 determines the number of frames that can be sent
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.
When configuring policing and policers, keep these items in mind:
• By default, no policers are configured.
• Policers can be configured only on a physical port or on a per-port per-VLAN basis (specifies the
bandwidth limits for the traffic on a per-VLAN basis, for a given port). Per-port per-VLAN policing
is not supported on routed ports or on virtual (logical) interfaces. It is supported only on an ingress
port configured as a trunk or as a static-access port.
Only one policer can be applied to a packet per direction.
•
• Only the average rate and committed burst parameters are configurable.
• Policing can occur on ingress and egress interfaces:
Note
–
–
–
–
On an interface configured for QoS, all traffic received through the interface is classified, policed,
•
and marked according to the policy map attached to the interface. On a trunk interface configured
for QoS, traffic in all VLANs received through the interface is classified, policed, and marked
according to the policy map attached to the interface.
After you configure the policy map and policing actions, attach the policy to an ingress or egress
interface by using the service-policy interface configuration command. For configuration information,
see the
the "Classifying, Policing, and Marking Traffic by Using Aggregate Policers" section on page
78-11194-09
Per-port per-VLAN policing is supported only on ingress interfaces.
128 policers are supported on ingress Gigabit-capable Ethernet ports.
8 policers are supported on ingress 10/100 Ethernet ports.
8 policers are supported on all egress ports.
Ingress policers can be individual or aggregate.
"Classifying, Policing, and Marking Traffic by Using Policy Maps" section on page 29-43
Catalyst 3550 Multilayer Switch Software Configuration Guide
Understanding QoS
and
29-49.
29-9