• Tail Drop
    • Default for all queues.
      • When queue full, new packets trying to enter the tail of queue are denied admission.
    • Tail drop treats all packets equally.
      • No classification is performed.
    • Tail drop can result in global TCP synchronization.
      • Simultaneous drops.
      • Looks like shark tooth.
      • Slow start by all senders at same time until they gradually begin going up again at same time. Then restart process.
  • Random Early Detection
    • Selectively drop flows from queue before buffer is 100% full.
    • Goal is to send individual senders into slow start, not all senders at once.
    • Result is more even traffic.
  • WRED adds weighting to Random Early Detection.
    • Higher weight means less likely to be dropped.
    • Configured as ‘random-detect’
      • Can be combined with other queueing mechanisms.

Configuration Example:

  • Create new Class-map

Create new Policy-map and add Class-map ‘SQL’ to the it.

And above we’re adding a bandwidth guarantee and then specifying ‘random-detect’ for WRED.

Note- A bandwidth command is required to enable random-detect.

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