350-001 · Question #127
350-001 Question #127: Real Exam Question with Answer & Explanation
The correct answer is B: The duplex settings are wrong on the Ethernet interface.. CBWFQ (Class-Based Weighted Fair Queuing) guarantees a minimum bandwidth expressed as an absolute value or percentage of the interface bandwidth. If the Ethernet interface is configured for half-duplex (or has a duplex mismatch between the router and the switch), the effective us
Question
Exhibit
Options
- AThe Ethernet interface should have keepalives enabled.
- BThe duplex settings are wrong on the Ethernet interface.
- CThe qos pre-classify command should be removed from the tunnel interfaces.
- Dthe priority queue for the voice class is probably taking all the bandwidth
- Ethere are probably not enough interface buffers; they should be tuned.
Explanation
CBWFQ (Class-Based Weighted Fair Queuing) guarantees a minimum bandwidth expressed as an absolute value or percentage of the interface bandwidth. If the Ethernet interface is configured for half-duplex (or has a duplex mismatch between the router and the switch), the effective usable bandwidth is dramatically reduced - often to less than half the nominal rate - due to collisions and the CSMA/CD backoff mechanism. A half-duplex interface on a 10 Mbps link may only sustain 3–4 Mbps of real throughput, making it impossible to guarantee 7 Mbps regardless of QoS configuration. The QoS policy itself may be correct, but the underlying physical layer problem prevents the guarantee from being met. Fixing the duplex to full-duplex eliminates collisions and allows the full bandwidth to be available.
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