What is used to perform QoS packet classification?

Question

Options

• Athe Options field in the Layer 3 header
• Bthe Type field in the Layer 2 frame
• Cthe Flags field in the Layer 3 header
• Dthe TOS field in the Layer 3 header

• A
  6% (3)
• B
  2% (1)
• C
  2% (1)
• D
  90% (44)

Explanation

QoS Packet Classification Explanation

Why D is correct: The Type of Service (TOS) field in the Layer 3 (IP) header is specifically designed to carry QoS markings, enabling routers and switches to classify and prioritize packets accordingly. In modern networks, this field is repurposed as the Differentiated Services (DSCP) field, which provides granular traffic classification for QoS policies.

Why the distractors are wrong:

• A (Options field): The IP Options field is used for special routing functions like source routing or timestamps - not QoS classification.
• B (Type field in Layer 2): The Ethernet Type field identifies the upper-layer protocol (e.g., IPv4, IPv6), not packet priority or QoS markings.
• C (Flags field): The IP Flags field controls fragmentation behavior (e.g., Don't Fragment), which has nothing to do with QoS classification.

Memory Tip: Think "TOS = Type Of Service = Quality Of Service" - the name itself tells you its purpose is to define how a packet should be treated (i.e., its service quality), making it the natural home for QoS classification markings.

No community discussion yet for this question.