Dell S4048-ON - Weighted Random Early Detection

Weighted Random Early Detection
Weighted random early detection (WRED) is a congestion avoidance mechanism that drops packets to prevent buering resources from
being consumed.
The WRED congestion avoidance mechanism drops packets to prevent buering resources from being consumed.
Trac 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 buer and trac manager (BTM) (ingress or egress) can be consumed by only one or a few types of trac, leaving no
space for other types. You can apply a WRED prole to a policy-map so that specied trac can be prevented from consuming too much
of the BTM resources.
WRED uses a prole to specify minimum and maximum threshold values. The minimum threshold is the allotted buer space for specied
trac, 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 buer space consumes less than 2000KB of the specied
trac.
Figure 111. Packet Drop Rate for WRED
You can create a custom WRED prole or use one of the ve pre-dened proles.
Table 78.
Pre-Dened WRED Proles
Default Prole Name Minimum Threshold Maximum Threshold Maximum Drop Rate
wred_drop 0 0 100
wred_teng_y 467 4671 100
wred_teng_g 467 4671 50
wred_fortyg_y 467 4671 50
wred_fortyg_g 467 4671 25
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