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350-401 Practice Question: An engineer configures IP SLA 100 to monitor the…
An engineer configures IP SLA 100 to monitor the jitter and latency of a VoIP call path between two branch routers. The configuration uses UDP jitter with a target of 192.168.2.2 on port 16384. The engineer notices that the IP SLA operation shows 'State: Active' but no jitter or latency statistics are collected. The router is generating the probe packets, but the remote router does not respond. What is the most likely reason?
⚠ Common exam trap
Cisco often tests the misconception that simply sending probes (State: Active) is enough to collect statistics, when in fact the IP SLA responder is mandatory for UDP jitter and other advanced operations that require two-way time-stamped communication.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The remote router must have an IP SLA responder configured to process the UDP jitter probes.
For UDP jitter IP SLA operations to collect jitter and latency statistics, the remote router must be configured as an IP SLA responder. The responder processes the probe packets and sends back time-stamped responses, which are essential for calculating jitter and one-way delay. Without the responder, the source router can send probes (showing 'Active' state) but cannot compute meaningful statistics because it never receives the required response packets.
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 must be configured with a 'request-data-size' value to match the remote router's MTU.
Why it's wrong here
The request-data-size parameter for a UDP jitter operation only controls the payload size of the probe packets; it is optional and does not affect whether the remote router answers. The IP SLA responder on the destination processes jitter probes regardless of the configured data size, so this setting has no bearing on the failure. An MTU mismatch is a separate forwarding issue and is not relevant to the absence of a responder.
- ✓
The remote router must have an IP SLA responder configured to process the UDP jitter probes.
Why this is correct
UDP jitter is a connectionless probe that depends on the remote router actively running the IP SLA responder service. The responder listens on a designated UDP port, timestamps each received packet, and echoes it back to the source so that one-way delay and jitter can be computed. Without this responder, there is no process bound to the destination port, so the probe packets are dropped or answered with an ICMP port unreachable rather than a valid IP SLA response.
- ✗
The source router needs a 'frequency' setting that matches the remote router's response interval.
Why it's wrong here
The frequency command on the source router determines how often the IP SLA operation sends a new probe iteration; it is purely a local scheduling knob and has no corresponding value that must be matched on the remote router. The responder does not maintain its own 'response interval' that needs to align with that frequency, and jitter calculation is unaffected by this scheduling parameter. Changing frequency only changes the sample interval, not whether the remote responder generates a response.
- ✗
The firewall on the remote router is blocking the UDP port 16384, preventing the probe from reaching the target.
Why it's wrong here
A firewall blocking UDP 16384 could prevent a jitter probe from arriving, but that is a secondary issue and not the root cause described by the need for a responder. Even if the firewall permitted the probe, the remote router would still need an IP SLA responder to listen on that port and generate the return traffic; otherwise the packet is simply discarded. Moreover, the presence of a firewall does not explain why the operation can never establish with the responder, because the responder is mandatory regardless of firewall state.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 350-401 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 350-401 exam.