CANOGA PERKINS 9175 Configuration Guide - Manual (Page 209)

CanogaOS Configuration Guide
31-3
The policer limits the bandwidth consumed by a traffic flow. The result is given to the
marker.
There are two types of policers:
• Individual: QoS applies the bandwidth limits specified in the policer, separately, to
each matched traffic class. An individual policer is configured within a policy map.
• Aggregate: QoS applies the bandwidth limits specified in an aggregate policer,
cumulatively, to all matched traffic flows. An aggregate policer is configured by
specifying the policer name within a policy map. The bandwidth limits of the
policer are specified. In this way, the aggregate policer is shared by multiple
classes of traffic within one or multiple policy map.
Policing and policers have the following attributes:
• Policers can occur only on a physical port basis.
• Policing can occur on ingress or egress of interfaces.
Marking
Marking determines how to handle a packet when it is out of profile. It assesses the
policer and the configuration information to determine the action required for the packet,
then handles the packet using one of the following methods:
• Let the packet through and mark color down
• Drop the packet
Marking can occur on ingress and egress interfaces.
Queueing
Queueing maps packets to a queue. Each egress port can accommodate up 8 queues,
prioritized as 0 lowest and 7 highest.
The packet internal priority can be mapped to one of the 8 queues obtained from the
filtering mechanism result.
After the packets are mapped to a queue, they are scheduled.
Tail Drop
Tail drop is the default congestion-avoidance technique on the interface. With tail drop,
packets are queued until the thresholds are exceeded. The packets with color red are
assigned to the first threshold for drop precedence 0, yellow are assigned to the second
threshold for drop precedence 1, and green are assigned to the third threshold for drop
precedence 2. You can modify the three tail-drop threshold to every egress queue by
using the queue threshold interface configuration command. Each threshold value is
packet number, which ranges from 0 to 64.
WRED
Weighted Random Early Detection (WRED) differs from other congestion-avoidance
techniques because it attempts to anticipate and avoid congestion, rather than
controlling congestion when it occurs.
WRED reduces the chances of tail drop by selectively dropping packets when the output
interface begins to show signs of congestion. By dropping some packets early rather
than waiting until the queue is full, WRED avoids dropping large numbers of packets at
once. Thus, WRED allows the transmission line to be fully used at all times. WRED also