Question 121 of 2,015

WAN Technologies →easyMultiple ChoiceObjective-mapped

Quick Answer

The answer is that the dialer interface does not have an IP address negotiated via IPCP. Even though the PPPoE session establishes and a default route appears in the routing table, the router cannot ping the ISP gateway because the dialer interface lacks a dynamically assigned IP address from the ISP. PPPoE relies on IP Control Protocol (IPCP) to negotiate the client’s IP address over the established PPP session; without this negotiation, the interface remains unnumbered or has no usable IP, making return traffic impossible. On the ENCOR 350-401 exam, this scenario tests your understanding of PPPoE client configuration and the distinction between session establishment and IP layer connectivity—a common trap is assuming a successful PPPoE session guarantees IP reachability. Remember: a default route via the dialer is useless if the interface itself has no IP address. Memory tip: “Session up, no IP? Check IPCP.”

350-401 WAN Technologies Practice Question

This 350-401 practice question tests your understanding of wan technologies. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 is configuring a PPPoE client on a Cisco router for a DSL connection. The engineer configures the dialer interface with the correct PPPoE profile and authentication credentials. The PPPoE session establishes, but the router cannot ping the ISP's gateway IP address. The engineer checks the routing table and sees that a default route is present via the dialer interface. What is the most likely cause?

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

Review the full routing breakdown →

A
The dialer interface does not have an IP address negotiated via IPCP.
Correct. In PPPoE, the ISP typically assigns an IP address via IPCP. If the dialer interface does not receive an IP address, the router cannot communicate with the gateway.
B
The physical interface is configured with 'no ip address'.
Why wrong: Incorrect. The physical interface does not need an IP address for PPPoE; the dialer interface handles the IP layer.
C
The default route is pointing to the wrong next-hop IP.
Why wrong: Incorrect. The default route via the dialer interface uses the interface itself as the next hop, not an IP address. This is typical for PPPoE.
D
The ISP's gateway is not responding to ICMP.
Why wrong: Incorrect. While possible, the most common cause is the missing IP address on the dialer interface. The scenario states the session is established, so the gateway is reachable at Layer 2.

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

✓

The dialer interface does not have an IP address negotiated via IPCP.

PPPoE sessions often require the use of PPPoE client configuration on the physical interface and the dialer interface. A common issue is that the physical interface (e.g., Ethernet) is not configured with the 'pppoe enable' command, or the dialer interface is not bound to the correct dialer pool. However, the session is established, so the PPPoE negotiation succeeded. The inability to ping the gateway is often due to a missing or incorrect 'ip route' or a firewall issue, but the most common cause is that the ISP requires the use of PPP IPCP to negotiate the IP address, and the router may not have an IP address assigned.

Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

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 dialer interface does not have an IP address negotiated via IPCP.
Why this is correct
Correct. In PPPoE, the ISP typically assigns an IP address via IPCP. If the dialer interface does not receive an IP address, the router cannot communicate with the gateway.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The physical interface is configured with 'no ip address'.
Why it's wrong here
Incorrect. The physical interface does not need an IP address for PPPoE; the dialer interface handles the IP layer.
✗
The default route is pointing to the wrong next-hop IP.
Why it's wrong here
Incorrect. The default route via the dialer interface uses the interface itself as the next hop, not an IP address. This is typical for PPPoE.
✗
The ISP's gateway is not responding to ICMP.
Why it's wrong here
Incorrect. While possible, the most common cause is the missing IP address on the dialer interface. The scenario states the session is established, so the gateway is reachable at Layer 2.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.

Trap categories for this question

Scenario analysis trap
Incorrect. While possible, the most common cause is the missing IP address on the dialer interface. The scenario states the session is established, so the gateway is reachable at Layer 2.

Detailed technical explanation

How to think about this question

This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.

KKey Concepts to Remember

Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
Use explanations to understand the rule behind the answer.

TExam Day Tips

Underline the problem statement mentally.
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

Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Real-world example

How this comes up in practice

A practitioner preparing for the 350-401 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.

What to study next

Got this wrong? Here's your next step.

Identify which 350-401 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.

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FAQ

Questions learners often ask

What does this 350-401 question test?

WAN Technologies — This question tests WAN Technologies — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: The dialer interface does not have an IP address negotiated via IPCP. — PPPoE sessions often require the use of PPPoE client configuration on the physical interface and the dialer interface. A common issue is that the physical interface (e.g., Ethernet) is not configured with the 'pppoe enable' command, or the dialer interface is not bound to the correct dialer pool. However, the session is established, so the PPPoE negotiation succeeded. The inability to ping the gateway is often due to a missing or incorrect 'ip route' or a firewall issue, but the most common cause is that the ISP requires the use of PPP IPCP to negotiate the IP address, and the router may not have an IP address assigned.

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?

Read the scenario before looking for a memorised answer.

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