350-501 · Question #246
The engineering team at a large ISP has been alerted a customer network is experiencing high traffic congestion. After a discussion between the ISP and technical personnel at the customer site, the…
The correct answer is D. Set IP precedence values to take effect when traffic exceeds a given threshold. To implement traffic policing that drops traffic exceeding a threshold due to congestion, the engineer must configure QoS policies to set IP precedence values or explicitly drop packets when the threshold is surpassed.
Question
The engineering team at a large ISP has been alerted a customer network is experiencing high traffic congestion. After a discussion between the ISP and technical personnel at the customer site, the team agrees that traffic to the customer network that exceeds a specific threshold will be dropped. Which task must the engineer perform on the network to implement traffic policing changes?
Options
- AConfigure RSVP to reserve bandwidth on all interfaces when a path is congested.
- BEnable Cisco Discovery Protocol on the interface sending the packets.
- CEnable Cisco Express Forwarding on the interfaces sending and receiving the packets.
- DSet IP precedence values to take effect when traffic exceeds a given threshold.
How the community answered
(43 responses)- A16% (7)
- B7% (3)
- C5% (2)
- D72% (31)
Why each option
To implement traffic policing that drops traffic exceeding a threshold due to congestion, the engineer must configure QoS policies to set IP precedence values or explicitly drop packets when the threshold is surpassed.
RSVP is a protocol used for reserving bandwidth to guarantee quality of service for specific application flows, not for policing and dropping excess traffic that exceeds a defined threshold.
Cisco Discovery Protocol (CDP) is a Layer 2 protocol used for discovering information about directly connected Cisco devices and is unrelated to traffic policing or congestion management.
Cisco Express Forwarding (CEF) is a high-performance Layer 3 IP forwarding mechanism and does not directly implement traffic policing or congestion management policies, although it is an underlying forwarding service.
Traffic policing involves defining actions for traffic that conforms or exceeds a specified rate. When traffic exceeds a given threshold, a common action is to drop the packets, or alternatively, to remark their IP precedence (or DSCP) value to a lower priority, signaling that they are eligible to be dropped by downstream devices, thus directly implementing the desired policy.
Concept tested: Traffic policing actions for exceeding thresholds (remarking/dropping)
Source: https://www.cisco.com/c/en/us/td/docs/ios/qos/configuration/guide/12_4/qos_12_4_book/qos_pol_shaping.html
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