Classification is the Quality of Service (QoS) mechanism responsible for inspecting incoming (ingress) traffic and categorizing it based on specific criteria. On a FortiSwitch, a QoS policy classifies packets by matching their existing Class of Service (CoS) or Differentiated Services Code Point (DSCP) markings. Based on this classification, the policy then maps the packet to a specific egress queue for prioritized transmission. This entire decision-making process of reading the markings and assigning a queue happens upon ingress.

A. Queuing for egress traffic: Queuing is the process of buffering packets in their assigned queues before transmission; it is the result of classification, not the mapping mechanism itself.

C. Rate limiting for egress traffic: Rate limiting (policing) controls the maximum rate of traffic by dropping excess packets. It does not map packets to queues based on their markings.

D. Marking for ingress traffic: Marking is the process of altering the CoS or DSCP value of a packet. The question asks about using existing markings for mapping, not changing them.

---

1. Fortinet FortiSwitch OS 7.6.0 Administration Guide, Page 178, "Quality of Service" chapter.

The guide states, "You can configure a quality of service (QoS) policy to classify, police, and mark incoming traffic." It further details the classification criteria: "You can classify incoming traffic by matching the 802.1p priority, the IP precedence, or the DSCP value." The action taken after classification includes set queue , which explicitly maps the classified traffic to an egress queue. This confirms classification happens on ingress to map to an egress queue.