D-Link DGS-3630 Emulator 1 - Page 1699

DGS-3630 Layer 3 Stackable Managed Switch CLI Reference Guide Default By default, this option is disabled. Command Mode 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 CE Bit Indicates 0 0 Not ECN capable, 0 1 ECN capable 1 0 ECN capable 1 1 Congestion experienced 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, 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 port 1 queue 5. Switch# configure terminal Switch(config)# interface eth1/0/1 Switch(config-if)# random-detect ecn 5 Switch(config-if)# 140-4 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 this command to revert to the default setting. random-detect exponential-weight COS-VALUE exponent VALUE no random-detect exponential-weight COS-VALUE Parameters COS-VALUE Specifies CoS queues on which the exponent will be set. The valid range is from 0 to 7. 1694