Question 492 of 2,015

IP SLA →easyMultiple ChoiceObjective-mapped

Quick Answer

The answer is that a stateful firewall or load balancer is responding to the TCP SYN on behalf of the server, causing the probe to succeed. This happens because an IP SLA TCP connect operation only verifies the completion of the TCP three-way handshake; it does not validate that the end server is actually processing requests. When a stateful device intercepts the SYN and replies with a SYN-ACK, the handshake completes successfully, so the IP SLA shows 'State: Active' and a low 'Latest RTT', even though the real server is down. On the ENCOR 350-401 exam, this scenario tests your understanding of how IP SLA probes interact with network security devices—a common trap is assuming a successful TCP connect confirms end-to-end server health. To remember, think of the firewall as a "fake friend" that answers the handshake for the server. Memory tip: "TCP connect checks the path, not the server's health."

CCNP IP SLA Practice Question

This 350-401 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.

An engineer configures IP SLA 50 to monitor the response time of a TCP connection to a server at 10.1.1.1 on port 80. The operation is used to trigger a backup path. The engineer notices that the IP SLA operation shows 'State: Active' and 'Latest RTT: 100 ms', but the server is actually down and not responding to TCP SYN packets. What is the most likely reason?

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.

Question 1easymultiple choice

Read the full NAT/PAT explanation →

A
A stateful firewall or load balancer is responding to the TCP SYN on behalf of the server, causing the probe to succeed.
Correct. If a network device intercepts the TCP handshake and responds, the IP SLA probe will consider the connection successful even if the actual server is down.
B
The IP SLA TCP connect probe does not actually verify that the server responds; it only checks if the port is open.
Why wrong: Incorrect because the TCP connect probe does perform a full three-way handshake; if a SYN-ACK is received, it considers the connection successful.
C
The IP SLA operation must be configured with a 'timeout' value lower than 100 ms to detect the failure.
Why wrong: Incorrect because the RTT is 100 ms, so a timeout lower than that would cause a false failure; the issue is that the probe is getting a response from a device other than the server.
D
The server is actually responding to the probe but not to other traffic because the probe uses a different source IP.
Why wrong: Incorrect because the probe uses the router's IP address as source, which is a legitimate source; the server would respond to it if it were up.

Full breakdown with real-world context →

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

✓

A stateful firewall or load balancer is responding to the TCP SYN on behalf of the server, causing the probe to succeed.

The TCP connect probe only checks if the TCP three-way handshake completes. If the server is down but a stateful firewall or load balancer responds to the SYN with a SYN-ACK, the probe will succeed even if the server is down.

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.

✓
A stateful firewall or load balancer is responding to the TCP SYN on behalf of the server, causing the probe to succeed.
Why this is correct
Correct. If a network device intercepts the TCP handshake and responds, the IP SLA probe will consider the connection successful even if the actual server is down.
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 IP SLA TCP connect probe does not actually verify that the server responds; it only checks if the port is open.
Why it's wrong here
Incorrect because the TCP connect probe does perform a full three-way handshake; if a SYN-ACK is received, it considers the connection successful.
✗
The IP SLA operation must be configured with a 'timeout' value lower than 100 ms to detect the failure.
Why it's wrong here
Incorrect because the RTT is 100 ms, so a timeout lower than that would cause a false failure; the issue is that the probe is getting a response from a device other than the server.
✗
The server is actually responding to the probe but not to other traffic because the probe uses a different source IP.
Why it's wrong here
Incorrect because the probe uses the router's IP address as source, which is a legitimate source; the server would respond to it if it were up.

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.

What to study next

Got this wrong? Here's your next step.

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 350-401 NAT questions on configuration and troubleshooting.

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FAQ

Questions learners often ask

What does this 350-401 question test?

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: A stateful firewall or load balancer is responding to the TCP SYN on behalf of the server, causing the probe to succeed. — The TCP connect probe only checks if the TCP three-way handshake completes. If the server is down but a stateful firewall or load balancer responds to the SYN with a SYN-ACK, the probe will succeed even if the server is down.

What should I do if I get this 350-401 question wrong?

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.

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