- A
The IP SLA operation uses a different source address than the ping command, causing the remote router to drop the packets due to uRPF.
Correct. A different source address can cause uRPF drop on the remote router, leading to timeout while ping from a different source succeeds.
- B
The IP SLA ICMP echo operation requires the IP SLA responder to be enabled on the remote router; without it, the operation may time out even if standard ping succeeds.
Why wrong: Incorrect. IP SLA ICMP echo does not require the responder; it works with standard ICMP. This is a common misconception.
- C
The IP SLA operation is blocked by an ACL on the local router that permits ICMP but denies IP SLA packets.
Why wrong: Incorrect. If an ACL on the local router blocks IP SLA packets, it would likely block ping as well since both are ICMP, unless the ACL specifically matches the IP SLA source IP, which is uncommon.
- D
The IP SLA operation has a frequency that is too high, causing the router to rate-limit the probes.
Why wrong: Incorrect. A high frequency may cause some probes to be sent before previous ones complete, but it does not typically cause timeouts; the router can handle parallel probes.
IP SLA ICMP Echo Timeout: Enable IP SLA Responder
This 300-410 practice question tests your understanding of ip sla. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. A key principle to apply: iP SLA ICMP Echo. 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.
An engineer configures IP SLA with an ICMP echo operation to track a remote host, but the IP SLA responder is not configured on the remote router. The IP SLA operation shows 'Timeout' in the show ip sla statistics output. The engineer expects the operation to succeed because the remote host is reachable via ping. 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.
Quick Answer
The answer is that the IP SLA ICMP echo operation requires the IP SLA responder to be enabled on the remote router, and without it, the operation will time out even when standard ping succeeds. This happens because IP SLA ICMP echo operations use a different packet processing path and timing mechanism than a basic ping; the responder ensures precise round-trip time measurement and proper packet handling, whereas a standard ping may succeed due to less strict timing or different ICMP processing. On the Cisco CCNP ENARSI 300-410 exam, this tests your understanding of IP SLA operation requirements versus simple connectivity verification—a common trap is assuming that reachability via ping guarantees IP SLA success. Remember the memory tip: “Ping proves path, but SLA needs a responder for the clock.”
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 IP SLA operation uses a different source address than the ping command, causing the remote router to drop the packets due to uRPF.
IP SLA ICMP echo operations do not require the IP SLA responder on the remote router; they rely on standard ICMP echo replies. When ping succeeds but IP SLA times out, a common cause is that the IP SLA process uses a different source IP address (e.g., the outgoing interface IP) than the ping command (which may use the closest interface IP). If the remote router has unicast Reverse Path Forwarding (uRPF) enabled, it may drop the IP SLA packets because the source address is not routable back via the same path, while the ping packet from a different source address may be allowed. Other possibilities like ACL blocking or rate-limiting are less likely because standard ICMP from ping works.
Key principle: IP SLA ICMP Echo
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 uses a different source address than the ping command, causing the remote router to drop the packets due to uRPF.
Why this is correct
Correct. A different source address can cause uRPF drop on the remote router, leading to timeout while ping from a different source succeeds.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
IP SLA ICMP Echo
- ✗
The IP SLA ICMP echo operation requires the IP SLA responder to be enabled on the remote router; without it, the operation may time out even if standard ping succeeds.
Why it's wrong here
Incorrect. IP SLA ICMP echo does not require the responder; it works with standard ICMP. This is a common misconception.
- ✗
The IP SLA operation is blocked by an ACL on the local router that permits ICMP but denies IP SLA packets.
- ✗
The IP SLA operation has a frequency that is too high, causing the router to rate-limit the probes.
Why it's wrong here
Incorrect. A high frequency may cause some probes to be sent before previous ones complete, but it does not typically cause timeouts; the router can handle parallel probes.
Common exam traps
Common exam trap: answer the scenario, not the keyword
IP SLA ICMP echo does not require the responder; timeout with successful ping often points to source address mismatch and uRPF issues.
Detailed technical explanation
How to think about this question
Treat this as a scenario question. Identify the problem, the constraint, and the best action. Then compare each option against those facts.
KKey Concepts to Remember
- IP SLA ICMP Echo
- Unicast Reverse Path Forwarding (uRPF)
- Source Address Selection
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
IP SLA ICMP Echo
Real-world example
How this comes up in practice
A security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
Visual reference
What to study next
Got this wrong? Here's your next step.
Review iP SLA ICMP Echo, then practise related 300-410 questions on the same topic to reinforce the concept.
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FAQ
Questions learners often ask
What does this 300-410 question test?
IP SLA — This question tests IP SLA — IP SLA ICMP Echo.
What is the correct answer to this question?
The correct answer is: The IP SLA operation uses a different source address than the ping command, causing the remote router to drop the packets due to uRPF. — IP SLA ICMP echo operations do not require the IP SLA responder on the remote router; they rely on standard ICMP echo replies. When ping succeeds but IP SLA times out, a common cause is that the IP SLA process uses a different source IP address (e.g., the outgoing interface IP) than the ping command (which may use the closest interface IP). If the remote router has unicast Reverse Path Forwarding (uRPF) enabled, it may drop the IP SLA packets because the source address is not routable back via the same path, while the ping packet from a different source address may be allowed. Other possibilities like ACL blocking or rate-limiting are less likely because standard ICMP from ping works.
What should I do if I get this 300-410 question wrong?
Review iP SLA ICMP Echo, then practise related 300-410 questions on the same topic to reinforce the concept.
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?
IP SLA ICMP Echo
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Last reviewed: Jun 19, 2026
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