Which of the following fields can be marked or remarked for frames belonging to a Layer 2 service?

Question

Options

• ADSCP
• BPREC
• CDot1p
• DToS
• EQ-in-Q

• A
  6% (2)
• B
  3% (1)
• C
  74% (23)
• D
  3% (1)
• E
  13% (4)

Explanation

Dot1p (IEEE 802.1p) is the correct answer because it is a 3-bit priority field embedded within the 802.1Q VLAN tag - making it a native Layer 2 construct that can be marked or remarked directly on Ethernet frames without requiring an IP header.

DSCP (A), IP Precedence/PREC (B), and ToS (D) are all Layer 3 fields residing in the IPv4 header; they are irrelevant to a pure Layer 2 service where there may be no IP payload to inspect or mark. Q-in-Q (E) is a VLAN stacking encapsulation technique (IEEE 802.1ad) used to tunnel customer VLANs across a provider network - it is not a QoS marking field at all.

Memory tip: Think "Dot1p = Dot1Q priority" - if the frame has a dot1Q tag, it has a dot1p priority field. Layer 2 = dot1p; Layer 3 = DSCP/ToS. Q-in-Q is the odd one out - it's about stacking tags, not marking them.

No community discussion yet for this question.