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- CCNA Routing and Switching 200-125
61.
If a traffic is marked with AF31 and another traffic pattern is marked with AF41,
which statement explains the traffic markings?
- A.AF31 marked traffic has a better queue than AF41 marked traffic.
- B.AF41 marked traffic has a better queue than AF31 marked traffic.
- C.Both AF31 and AF41 marked traffic has an equal queue.
- D.During high congestion, AF41 queues will be dropped and AF31 queues won’t.
- Answer & Explanation
- Report
Answer : [B]
Explanation :
Explanation :
| AF41 marked traffic has a better position in the queue than traffic marked AF31. During high congestion times, traffic with lower positions in the queues (AF3x, AF2x, AF1x) would have more chances of being dropped than AF41. |
62.
Which command on a Cisco switch will show the default CoS value?
- A.Switch#show qos interface
- B.Switch#show mls qos interface
- C.Switch#show interface
- D.Switch#show qos
- Answer & Explanation
- Report
Answer : [B]
Explanation :
Explanation :
| The command show mls qos interface will display information related to the current QoS trust level on the interface along with the default CoS value. |
63.
How do congestion avoidance tools help to prevent tail drop?
- A.When the queue depth is full, a percentage of TCP packets are dropped.
- B.When the queue depth is empty, a percentage of TCP packets are dropped
- C.When the queue depth is below the minimum threshold, a percentage of TCP packets are dropped.
- D.When the queue depth is above the minimum threshold, a percentage of TCP packets are dropped.
- Answer & Explanation
- Report
Answer : [D]
Explanation :
Explanation :
| When the queue depth is above the minimum threshold, a percentage of TCP packets are dropped. This allows the TCP window to shrink and allows a normal slowdown of TCP transmissions. This is done in hopes that the queue will fall under the minimum threshold and return to normal. |
64.
When configuring QoS for packet shaping, which is an important guideline to
follow?
- A.Always make the bit rate small.
- B.Always make the time interval small.
- C.Always make the time interval large.
- D.Always use the maximum bit rate.
- Answer & Explanation
- Report
Answer : [B]
Explanation :
Explanation :
| QoS packet shapers work by measuring traffic over a time interval. If the time interval is too large, the packets will be sent in the initial start of the interval. Then the router will wait until the interval is over to transmit again. Configuring a small time interval is desired so that the router is not waiting for the next interval to send packets. It is recommended to use a time interval of 10 milliseconds (ms) for voice and video traffic. |
65.
Which command will allow the CoS value to be trusted for a VoIP phone?
- A.Switch(config-if)#auto qos trust cos
- B.Switch(config-if)#qos trust cos
- C.Switch(config-if)#cos trust qos
- D.Switch(config-if)#auto qos
- Answer & Explanation
- Report
Answer : [A]
Explanation :
Explanation :
| The command auto qos trust cos will configure the interface to be trusted for the CoS value. This type of QoS will happen at layer 2 with the CoS field. Based upon the CoS value, the interface will be trusted for QoS. Normally, devices should not be trusted for QoS since the CoS value could be forged so that the user can gain preferential treatment of their packets. |
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