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Routing & Switching · Intermediate

Assured Forwarding (AF)

A DiffServ PHB group of four classes (AF1-AF4) each with three drop precedences (AFx1-AFx3).

Definition

Higher class numbers get more bandwidth assurance; within a class, higher drop precedence is dropped first by WRED. AF11 = 10, AF12 = 12, AF13 = 14 ... AF41 = 34, AF42 = 36, AF43 = 38.

Example

Transactional data marked AF21 (18) and remarked AF22 when exceeding contract.

Exam tip

In AFxy, x is the class and y the drop probability; AF13 drops before AF11.

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