Dell N1100-ON, Reference Manual

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Layer 2 Switching Commands
704
Command Mode
Global Configuration mode, Interface Configuration mode (physical and
port-channel), Interface Range mode
User Guidelines
Interface configuration overrides the global configuration.
WRED Processing
WRED is intended to provide feedback to protocols (e.g. TCP) that depend
on packet loss to adjust their transmission rate. WRED drop behavior only
occurs when an interface is congested within the ranges specified. If
congestion exceeds the upper limit, queued packets will be dropped at the
rate of traffic ingressing the system, e.g. 100%. If the congestion is less than
the lower limit, no packets will be dropped.
Traffic ingressing the switch can be assigned to one of four drop precedences
based on a set of matching criteria. There are 3 drop precedences for TCP
traffic (green, yellow, and red) and one drop precedence for non-TCP traffic
(all colors). Users may configure the congestion thresholds at which packets
experiencing congestion are dropped randomly for each drop precedence and
may also configure the probability of a packet being dropped.
Packets are dropped at 100% when the egress queue size exceeds the
maximum value and at 0% when the queue size is below the minimum value.
Configuring a queue with a drop probability of 0% effectively applies tail-drop
behavior when the queue length exceeds the maximum threshold.
If the max-thresh parameter is less than the corresponding min-thresh
parameter, it is adjusted to be the min-thresh plus one.
For a given network, the minimum and maximum WRED thresholds should
be calculated to give a reasonable amount of buffering to TCP flows given the
switch buffer capacity. WRED thresholds are applied individually to each
5 40/30/20/100 100/ 90/ 80/100 10/ 10/ 10/ 10 No
6 40/30/20/100 100/ 90/ 80/100 10/ 10/ 10/ 10 No
Queue ID WRED Minimum
Threshold
WRED Maximum
Threshold WRED Drop
Probability Scale ECN Enabled