The Congestion Action determines how a backed-up send queue is handled. Since this queue cannot grow indefinitely, packets must be discarded at some point. Two mechanisms are available here: Taildrop and Random Early Detection (RED) , also known as Random Early Discard. With taildrop, a limit is set beyond which all further incoming packets are discarded. In RED, two limits are determined. As of the first one, packets are discarded with a probability P. P increases the closer you get to the second limit. If the second limit is exceeded, all incoming packets are discarded, like taildrop.
The table Congestion-Action is defined in such a way that it can be configured to contain RED and Taildrop. This decision ensures maximum flexibility, on the one hand, but also a high potential for errors leading to a non-functional configuration. Hence the following explanation of the framework conditions for both concepts. A Taildrop is recognized by the fact that Threshold-Min is equal to Threshold-Max. Max-Probability with a Taildrop has no purpose, but should be entered as 100 to indicate that everything above the limit will be discarded. For a user to configure a Taildrop as easily as possible, a shortened input can be used:
root@:/Setup/WAN/QoS > add Congestion-Action/test bytes 2000 set ok: Name Metric-Type Threshold-Min Threshold-Max Max-Probability-Percentage ======================------------------------------------------------------------------------------ TEST Bytes 2000 2000 100
You only specify the Metric-Type and Limit-Min, the other values are set so that a Taildrop is configured.
For a RED, the Threshold-Min is not equal to Threshold-Max. The packet is discarded as of Threshold-Min starting with a probability P=0, where P linearly approaches Max-Probability the closer you get to Threshold-Max.
- SNMP ID:
- 2.2.71.1
- Console path:
- Setup > WAN > QoS
