D-Link DXS-3600 Series Reference Manual page 1280

DXS-3600 Series Layer 3 Managed 10Gigabit Ethernet Switch CLI Reference Guide
Interface Configuration Mode.
Command Default Level
Level: 12.
Usage Guideline
WRED drops packets, based on the average queue size exceeding a specific threshold, to indicate
congestion. ECN is an extension to WRED in that ECN marks packets instead of dropping them when the
average queue size exceeds a specific threshold value. When configuring the WRED Explicit Congestion
Notification feature, routers and end hosts would use this marking as a signal that the network is
congested and slow down sending packets.
As stated in RFC 3168 (ECN to IP), the ECN field has two bits. The ECN-capable transport (ECT) bit and
the Congestion Experienced (CE) bit in the IP header. Each of the ECT and CE bits combination list as
follows:
ECT Bit
0
0
1
1
The following points explain how packets are treated when ECN is enabled:
•
If the ECT and CE bit is (0,0), the packets are dropped based on the WRED drop probability.
•
If the ECT and CE bit is (0,1) or (1,0), the WRED determines that the packet should be dropped
based on the drop probability, then the ECT and CE bits for the packet are changed to 1 instead
of dropping them, and the packet is transmitted.
•
If the ECT and CE bit is (1,1), the packet is transmitted. No further marking is required
Example
This example shows how to enable ECN on eth 3/0/1 queue 5.
Switch# configure terminal
Switch(config)# interface eth3/0/1
Switch(config-if)# random-detect ecn 5
Switch(config-if)#
116-4 random-detect exponential-weight
This command is used to configure the WRED exponential weight factor for the average queue size
calculation for the queue. Use the no form of the command to reset to the default setting.
random-detect exponential-weight COS-VALUE exponent VALUE
no random-detect exponential-weight COS-VALUE
Parameters
COS-VALUE
exponent VALUE
Default
CE Bit Indicates
0 Not ECN capable,
1 ECN capable
0 ECN capable
1 Congestion experienced
Specifies CoS queues on which the exponent will be set. The valid
range is from 0 to 7.
Specifies the exponent value from 0 to 15.
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