The answer is that the IP SLA initiator must be configured with the control keyword to match the non-default control port on the responder. This is because IP SLA UDP echo operations rely on a dedicated control channel, using UDP port 1967 by default, to negotiate test parameters and synchronize the probe. When the responder’s control port is changed to a non-default value, the initiator still attempts to communicate on port 1967, causing the responder to ignore the setup messages—leading to intermittent timeouts even though standard UDP connectivity succeeds. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of the IP SLA responder architecture and the critical distinction between the data-plane echo port and the control-plane negotiation port. A common trap is assuming that a successful ping or UDP test to the target IP means the IP SLA operation should work, but the timeout actually stems from a control port mismatch, not a reachability issue. Remember the memory tip: “Control the control port” — if the responder changes its control port, the initiator must explicitly match it with the control keyword.
300-410 IP SLA Practice Question
This 300-410 practice question tests your understanding of ip sla. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A network engineer configures IP SLA with a UDP echo operation to monitor a remote server. The IP SLA responder is configured on the remote router. The engineer notices that the operation shows 'Timeout' intermittently, but standard UDP connectivity tests from the router to the server succeed. The engineer checks the IP SLA responder configuration and finds that the control port is set to a non-default value. Which is the most likely explanation?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The IP SLA initiator must be configured with the 'control' keyword to match the non-default control port on the responder.
IP SLA UDP echo operations require the IP SLA responder to be configured with the correct control port. If the responder uses a non-default control port, the initiator must be configured to use that port using the 'control' keyword under the IP SLA operation. Without this, the initiator uses the default control port (1967), causing communication failures and intermittent timeouts.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 responder is not configured to respond to UDP echo requests from the initiator.
Why it's wrong here
The responder is configured, but the control port mismatch prevents proper setup.
✓
The IP SLA initiator must be configured with the 'control' keyword to match the non-default control port on the responder.
Why this is correct
The control port mismatch causes the initiator to fail to establish the operation, leading to timeouts.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
✗
The UDP echo operation uses a different protocol than standard UDP, causing packet drops.
Why it's wrong here
UDP echo uses standard UDP; the issue is control port.
✗
The IP SLA operation has a threshold that is too low, causing the operation to time out.
Why it's wrong here
Threshold does not cause timeouts; timeout does.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
How this comes up in practice
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 300-410 NAT questions on configuration and troubleshooting.
IP SLA — This question tests IP SLA — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: The IP SLA initiator must be configured with the 'control' keyword to match the non-default control port on the responder. — IP SLA UDP echo operations require the IP SLA responder to be configured with the correct control port. If the responder uses a non-default control port, the initiator must be configured to use that port using the 'control' keyword under the IP SLA operation. Without this, the initiator uses the default control port (1967), causing communication failures and intermittent timeouts.
What should I do if I get this 300-410 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 300-410 NAT questions on configuration and troubleshooting.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
About these practice questions
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These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. An engineer configures IP SLA with a UDP jitter operation to monitor VoIP quality between two routers. The operation shows 'OverThreshold' in the show ip sla statistics output, but the engineer notices that the IP SLA responder on the remote router is configured with a control port that does not match the default. Which is the most likely explanation?
hard
A.The IP SLA responder control port mismatch causes the operation to use a different port, but the jitter calculation is unaffected.
✓ B.The IP SLA initiator must be configured with the 'control' keyword to specify the non-default control port on the responder.
C.The IP SLA responder automatically adjusts its control port to match the initiator's request.
D.The UDP jitter operation does not use the control port; it only uses the destination port for jitter probes.
Why B: IP SLA UDP jitter operations require the IP SLA responder to be configured with the correct control port; if the responder uses a non-default control port, the IP SLA initiator must be configured to use that port via the 'control' keyword under the IP SLA operation, otherwise the operation fails or produces incorrect results.
Last reviewed: Jun 19, 2026
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