350-401 Practice Question: Configures IP SLA 60 to monitor the jitter of a…

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✓

  The IP SLA operation is configured with a 'num-packets' value of 1, so only one packet is sent per probe, and jitter cannot be calculated.

  Why this is correct

  This is the correct diagnosis. For the IP SLA UDP jitter operation (type 'udp-jitter'), the source router sends a burst of packets per probe—by default 10—and measures the inter-arrival time differences among the returned packets to compute jitter. If the engineer set the 'num-packets' parameter to 1, only a single packet is sent per probe, so there are no two consecutive packets from which to calculate delay variation. The result is that jitter is reported as zero, not because the network has no variation, but because the probe lacks the required packet pair.

• ✗

  The remote router's IP SLA responder is not configured to calculate jitter, only to echo packets.

  Why it's wrong here

  This is incorrect because the remote IP SLA responder is not responsible for calculating jitter; it merely receives each probe packet, timestamps it, and sends it back to the source (or echoes it). Jitter is always computed by the source router using the timestamps of multiple packets it receives back. Even if the responder were not configured to operate in a special jitter mode, the source can still calculate jitter from the received packets—the responder's role is only to return the packets with accurate timing. The absence of a responder would cause the probe to fail entirely, not to produce zero jitter.

• ✗

  The IP SLA operation is using a 'frequency' that is too high, causing the probes to be sent too quickly and jitter to be zero.

  Why it's wrong here

  This is incorrect because 'frequency' controls how often a probe (i.e., a complete burst of packets) is initiated, not how many packets are sent inside each burst. A very high frequency—meaning a short interval between probes—might cause probes to overlap or be sent back-to-back, but each probe would still contain its configured 'num-packets' (e.g., 10). Jitter is calculated from the packets within a single probe, not across separate probes, so the frequency setting has no direct impact on whether jitter can be computed. The real reason for a zero jitter value is the single-packet payload, not the probe scheduling rate.

• ✗

  The network path has no variable delay, so jitter is naturally zero.

  Why it's wrong here

  This is incorrect because while a perfectly constant network path could theoretically produce zero jitter, that is extremely rare in real-world IP networks due to variable queueing delays, processing times, and routing hops. The more immediate and deterministic cause is the configuration: with 'num-packets 1', jitter will be reported as zero regardless of the network's actual delay characteristics. Even if the network had measurable delay variation, a single-packet probe could not capture it. Thus, attributing zero jitter to a stable path overlooks the unambiguous configuration issue, which is the root cause.

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