Refer to the exhibit. You would like to guarantee 7 Mb/s for FTP traffic in your LAN, as it seems that peer-to-peer traffic is taking up a large amount of bandwidth. When testing the configuration…

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.

• A
  3% (1)
• B
  76% (28)
• C
  3% (1)
• D
  14% (5)
• E
  5% (2)

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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