Cisco IE 3000 User Manual

32-8
Cisco IE 3000 Switch Software Configuration Guide
OL-13018-01
Chapter 32 Configuring QoS
Understanding QoS
Policing and Marking
After a packet is classified and has a DSCP-based or CoS-based QoS label assigned to it, the policing
and marking process can begin as shown in
Figure 32-4.
Policing involves creating a policer that specifies the bandwidth limits for the traffic. Packets that exceed
the limits are out of profile or nonconforming. Each policer decides on a packet-by-packet basis whether
the packet is in or out of profile and specifies the actions on the packet. These actions, carried out by the
marker, include passing through the packet without modification, dropping the packet, or modifying
(marking down) the assigned DSCP of the packet and allowing the packet to pass through. The
configurable policed-DSCP map provides the packet with a new DSCP-based QoS label. For information
on the policed-DSCP map, see the
“Mapping Tables” section on page 32-10. Marked-down packets use
the same queues as the original QoS label to prevent packets in a flow from getting out of order.
Note All traffic, regardless of whether it is bridged or routed, is subjected to a policer, if one is configured.
As a result, bridged packets might be dropped or might have their DSCP or CoS fields modified when
they are policed and marked.
You can configure policing on a physical port. For more information about configuring policing on
physical ports, see the
“Policing on Physical Ports” section on page 32-8.
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 on Physical Ports by Using Policy Maps” section on page 32-44 and the
“Classifying, Policing, and Marking Traffic by Using Aggregate Policers” section on page 32-47.
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.
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.

Cisco IE 3000 Specifications

General

Operating Temperature	-40 to 75°C (-40 to 167°F)
DRAM	128 MB
Flash Memory	32 MB
Uplink Ports	2 x 10/100/1000Base-T or SFP
MAC Address Table Size	8000
Mounting	DIN rail, Wall