CCNA/CCNP preparation notes

by Andreas Ryf

Congestion Avoidance

Tail drop

Any arriving packet that doesn't have space in the queue gets dropped.

Problem: Packets of high priority that meet a full queue are dropped despite their priority.

RED - Random Early Detection

Starts randomly dropping packets before the queues are full

Does not control what packets are dropped

Not very advantageous for VoIP

WRED - Weighted Random Early Detection

Cisco's implementation which considers the types of packets to be dropped preferrably

At the maximum thershold Tail Dropping sets in again

ECN - Explicit Congestion Notification

Uses last two TOS-Bits.

Proactive instead of reactive

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