33-10
Catalyst 2975 Switch Software Configuration Guide
OL-19720-02
Chapter 33 Configuring QoS
Understanding QoS
Policing on Physical Ports
In policy maps on physical ports, you can create these types of policers:
•
Individual—QoS applies the bandwidth limits specified in the policer separately to each matched
traffic class. You configure this type of policer within a policy map by using the
police
policy-map
class configuration command.
•
Aggregate—QoS applies the bandwidth limits specified in an aggregate policer cumulatively to all
matched traffic flows. You configure this type of policer by specifying the aggregate policer name
within a policy map by using the
police aggregate
policy-map class configuration command. You
specify the bandwidth limits of the policer by using the
mls qos aggregate-policer
global
configuration command. In this way, the aggregate policer is shared by multiple classes of traffic
within a policy map.
Note
You can configure only individual policers on an SVI.
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-b/s), 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.
Содержание 2975 - Catalyst LAN Base Switch
Страница 36: ...Contents xxxvi Catalyst 2975 Switch Software Configuration Guide OL 19720 02 ...
Страница 40: ...xxxviii Catalyst 2975 Switch Software Configuration Guide OL 19720 02 Preface ...
Страница 62: ...1 22 Catalyst 2975 Switch Software Configuration Guide OL 19720 02 Chapter 1 Overview Where to Go Next ...
Страница 398: ...13 30 Catalyst 2975 Switch Software Configuration Guide OL 19720 02 Chapter 13 Configuring VLANs Configuring VMPS ...
Страница 424: ...15 18 Catalyst 2975 Switch Software Configuration Guide OL 19720 02 Chapter 15 Configuring VTP Monitoring VTP ...
Страница 628: ...26 8 Catalyst 2975 Switch Software Configuration Guide OL 19720 02 Chapter 26 Configuring UDLD Displaying UDLD Status ...
Страница 660: ...28 8 Catalyst 2975 Switch Software Configuration Guide OL 19720 02 Chapter 28 Configuring RMON Displaying RMON Status ...
Страница 888: ...38 32 Catalyst 2975 Switch Software Configuration Guide OL 19720 02 Chapter 38 Troubleshooting Troubleshooting Tables ...