Weighted Random Early Detection - Dell S4048–ON Configuration Manual

Weighted Random Early Detection

Weighted random early detection (WRED) is a congestion avoidance mechanism that drops packets to prevent buffering resources from
being consumed.
The WRED congestion avoidance mechanism drops packets to prevent buffering resources from being consumed.
Traffic is a mixture of various kinds of packets. The rate at which some types of packets arrive might be greater than others. In this case,
the space on the buffer and traffic manager (BTM) (ingress or egress) can be consumed by only one or a few types of traffic, leaving no
space for other types. You can apply a WRED profile to a policy-map so that specified traffic can be prevented from consuming too much
of the BTM resources.
WRED uses a profile to specify minimum and maximum threshold values. The minimum threshold is the allotted buffer space for specified
traffic, for example, 1000KB on egress. If the 1000KB is consumed, packets are dropped randomly at an exponential rate until the maximum
threshold is reached (as shown in the following illustration); this procedure is the "early detection" part of WRED. If the maximum threshold,
for example, 2000KB, is reached, all incoming packets are dropped until the buffer space consumes less than 2000KB of the specified
traffic.
Figure 111. Packet Drop Rate for WRED
You can create a custom WRED profile or use one of the five pre-defined profiles.
Table 78. Pre-Defined WRED Profiles
Default Profile Name
wred_drop
wred_teng_y
wred_teng_g
wred_fortyg_y
wred_fortyg_g
748 Quality of Service (QoS)
Minimum Threshold
0
467
467
467
467
Maximum Threshold
0
4671
4671
4671
4671
Maximum Drop Rate
100
100
50
50
25