Implementing Cisco Networking Solutions

Tail drop

Tail drop is the default congestion avoidance behavior when WRED is not configured. Tail drop treats all traffic equally and does not differentiate between packet types within the same queue. Queues get filled during periods of traffic congestion. When the output queue is full and tail drop is in effect, packets are dropped from the tail of the queue until the congestion is eliminated and the queue is no longer full.

This dropping of packets in a TCP stream leads to the end nodes reducing their TCP window size, thereby sending less traffic on the network. Packet drops in TCP help control congestion at the source itself. UDP packets on the other hand have no acknowledgement and flow control, and hence are immune to any packet drops, ...