350-401 Question #55: Real Exam Question with Answer & Explanation

Question

Which marking field is used only as an internal marking within a router?

Options

• AQOS Group
• BDiscard Eligiblity
• CIP Precedence
• DMPLS Experimental

Explanation

QoS Group is correct because it is a locally significant marking used only within a single router - it is never carried in the packet header or transmitted to other devices. It allows a router to internally classify and mark traffic for policy decisions without modifying any actual packet field.

Why the distractors are wrong:

• Discard Eligibility (B) is a bit in the Frame Relay header used to mark frames that can be dropped during congestion - it travels with the frame across the network.
• IP Precedence (C) is carried in the IP packet header (the first 3 bits of the ToS byte) and is transmitted end-to-end across the network.
• MPLS Experimental/EXP (D) is carried in the MPLS label header and is passed between MPLS-enabled devices along the label-switched path.

Memory Tip: Think of QoS Group as a sticky note a router writes to itself - it's internal scratch paper that never leaves the building. If a marking travels in a packet header to another device, it's NOT a QoS Group. The phrase "Group stays home" can help you remember its locally significant nature.

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