300-070 Question #114: Real Exam Question with Answer & Explanation

Question

Options

• ADSCP CS3.
• BDSCP 0.
• CDSCP AF11.
• DDSCP CS6.
• EDSCP EF.
• FDSCP CS2.
• GDSCP CS1.
• HDSCP AF21.

Explanation

RFC 2474 defines the Differentiated Services field and the Class Selector (CS) Per-Hop Behavior codepoints, which use a binary 'xxx000' pattern in the 6-bit DSCP field.

Common mistakes.

• B. DSCP 0 represents default best-effort forwarding and while referenced in RFC 2474, it is not a distinctly defined named classification codepoint - it is the absence of any specific traffic marking.
• C. DSCP AF11 belongs to the Assured Forwarding PHB group defined in RFC 2597, not RFC 2474.
• D. DSCP CS6 is also a Class Selector codepoint technically in RFC 2474, but it is most prominently associated with routing protocol and network control traffic per Cisco QoS design guides and RFC 4594, making it context-specific rather than the primary RFC 2474 example.
• E. DSCP EF (Expedited Forwarding) is defined in RFC 3246, which superseded the original EF definition in RFC 2598, not in RFC 2474.
• F. DSCP CS2 is also a Class Selector codepoint in RFC 2474 but is more commonly associated with OAM traffic per RFC 4594 design guidance, making it a secondary context rather than the primary RFC 2474 tested concept.
• G. DSCP CS1 is also a Class Selector codepoint in RFC 2474 but is commonly mapped to scavenger/lower-than-best-effort traffic per Cisco QoS design guides, making it a secondary context rather than the primary RFC 2474 tested concept.
• H. DSCP AF21 belongs to the Assured Forwarding PHB group defined in RFC 2597, not RFC 2474.

Concept tested. RFC 2474 Differentiated Services Class Selector codepoints

Reference. https://datatracker.ietf.org/doc/html/rfc2474

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