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Objective 4.7

200-301

Explain the forwarding per-hop behavior (PHB) for QoS such as classification, marking, queuing, congestion, policing, and shaping.

Objective 4.7 sits in IP Services, which carries 10% of the CCNA exam. The questions below are original, written from the official objective title above, and each explanation cites the Cisco page it rests on.

Objective title verbatim from the official objectives. Cisco exam page ↗

A worked example

Shown solved, with the whole explanation open: this is what every question here carries.

4-7IP Services

A campus edge switch marks voice traffic with a DSCP value, and the core routers you manage are configured to queue only on the DS field. What does the six-bit codepoint select at each core node?

The bandwidth reserved end to end for the flowEnd-to-end reservation is what a signaling protocol such as RSVP sets up. Differentiated services deliberately hold no reservation state for a flow.
The per-hop behavior applied to that behavior aggregateCorrect · your answerCorrect. The codepoint picks the treatment given to that aggregate at every node.
The output interface chosen from the routing tableForwarding still follows the destination address and the routing table. The DS field changes how a packet is queued, not where it is sent.
The queue depth advertised to the upstream neighborNothing in the DS field is advertised anywhere. Queue depth is local configuration on the node doing the queuing and is never carried in the header.

Correct.

Checked against datatracker.ietf.org, August 2026

Concept

Differentiated services keep per-flow state out of the core. A node reads one header field, maps its value to a forwarding treatment it already implements, and needs no signaling and no knowledge of individual conversations to do it.

Why B

Marking sets the value at the boundary; from there the codepoint acts as an index. Each compliant node matches the whole six-bit field, as a table index rather than a range, and applies the treatment it holds for that value, independently of what any other node along the path decides.

Source

Six bits of the DS field are used as a codepoint (DSCP) to select the PHB a packet experiences at each node.

IETF RFC 2474: Definition of the Differentiated Services Field, checked August 2026
#qos#dscp#per-hop-behavior

Now you: objective 4.7 questions

No account needed. The explanation opens when you answer.

Sample question 1 of 3

4-7IP ServicesChoose 2

An engineer marks branch traffic for assured forwarding on a WAN edge and must plan the marking scheme. Which two properties does the AF group give? (Choose two.)

Sample question 2 of 3

4-7IP Services

Voice packets are marked with a DSCP value at the network edge. Where does the design expect marking to happen?

Sample question 3 of 3

4-7IP Services

A router applies a defined forwarding treatment to each packet based on its DSCP mark. What is that treatment called?

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Read the sources

These are the official pages the questions above cite. Reading them is studying the objective from the primary source, which is what the explanations point you toward anyway.

More objectives in IP Services