Which DSCP classification is defined in RFC 2474?

DSCP CS3 is a Class Selector codepoint (binary 011000, decimal 24) defined in RFC 2474, which established the Differentiated Services Code Point framework and all CS0 through CS7 codepoints. RFC 2474 is the foundational document that introduced the CS PHB class, with each CS value following the 'xxx000' bit pattern to maintain backward compatibility with IP Precedence.

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.

DSCP AF11 belongs to the Assured Forwarding PHB group defined in RFC 2597, not RFC 2474.

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.

DSCP EF (Expedited Forwarding) is defined in RFC 3246, which superseded the original EF definition in RFC 2598, not in RFC 2474.

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.

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.

DSCP AF21 belongs to the Assured Forwarding PHB group defined in RFC 2597, not RFC 2474.