- A
The workstation's default gateway is set to 10.0.0.1.
Why wrong: The workstation can ping the router, so the gateway is correctly set to 10.0.0.1.
- B
The router lacks a default route pointing to the ISP's gateway.
Without a default route, the router does not know where to send traffic destined for the internet, even though it has a WAN IP.
- C
The WAN subnet mask should be 255.255.255.0.
Why wrong: The ISP provided a /30 subnet, which is correct for a point-to-point link; changing it would break connectivity.
- D
The LAN subnet mask should be 255.255.0.0.
Why wrong: The /24 mask is appropriate for the LAN and allows communication; changing it would not fix the internet issue.
Question 986 of 1,020
Why a Router with WAN IP Can't Access the Internet Without Default Route
This 220-1201 practice question tests your understanding of ip addressing. 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 technician is configuring a router with two interfaces: WAN (DHCP from ISP) and LAN (static IP 10.0.0.1/24). The technician sets the LAN subnet mask to 255.255.255.0. A workstation is assigned IP 10.0.0.100/24 and can ping the router, but cannot access the internet. The router's WAN interface has IP 203.0.113.5/30. What is the most likely missing configuration?
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 router lacks a default route pointing to the ISP’s gateway. Even with a valid WAN IP address like 203.0.113.5/30, the router has no path to forward traffic beyond its directly connected subnet; a default route (0.0.0.0/0) tells the router where to send packets destined for the internet. On the CompTIA A+ Core 1 220-1201 exam, this scenario tests your understanding of routing fundamentals and the difference between having an IP address and having a functional path to the internet—a common trap is assuming a DHCP-assigned WAN IP automatically includes a default route, but if the ISP’s gateway isn’t specified or the route is missing, traffic stalls. Remember, a router with a WAN IP but no default route is like a car with a full tank of gas but no map; it has the means to move but no direction. Memory tip: “No route, no root” — without a default route, there’s no root path to the internet.
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 router lacks a default route pointing to the ISP's gateway.
The workstation can ping the router's LAN interface (10.0.0.1), confirming Layer 2 and basic IP connectivity on the LAN. However, for the workstation to reach the internet, the router must have a default route (0.0.0.0/0) pointing to the ISP's next-hop gateway (likely 203.0.113.6, the other end of the /30 WAN link). Without this route, the router does not know where to forward packets destined for external networks, even though the WAN interface has a valid IP from DHCP.
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 workstation's default gateway is set to 10.0.0.1.
Why it's wrong here
The workstation can ping the router, so the gateway is correctly set to 10.0.0.1.
- ✓
The router lacks a default route pointing to the ISP's gateway.
Why this is correct
Without a default route, the router does not know where to send traffic destined for the internet, even though it has a WAN IP.
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 WAN subnet mask should be 255.255.255.0.
Why it's wrong here
The ISP provided a /30 subnet, which is correct for a point-to-point link; changing it would break connectivity.
- ✗
The LAN subnet mask should be 255.255.0.0.
Why it's wrong here
The /24 mask is appropriate for the LAN and allows communication; changing it would not fix the internet issue.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that a workstation being able to ping the router's LAN interface implies full internet connectivity, when in fact the router itself lacks a route to forward traffic beyond its directly connected networks.
Detailed technical explanation
How to think about this question
When a router receives a packet destined for a non-local network, it performs a longest-prefix match against its routing table. Without a default route (0.0.0.0/0), the router will drop the packet and send an ICMP Destination Unreachable (Network Unreachable) back to the source. In production networks, the default route is often learned via DHCP on the WAN interface (option 3, Router) or statically configured; if DHCP fails to provide a gateway, the technician must manually add 'ip route 0.0.0.0 0.0.0.0 203.0.113.6'.
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.
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
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 network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
Visual reference
What to study next
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FAQ
Questions learners often ask
What does this 220-1201 question test?
IP Addressing — This question tests IP Addressing — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The router lacks a default route pointing to the ISP's gateway. — The workstation can ping the router's LAN interface (10.0.0.1), confirming Layer 2 and basic IP connectivity on the LAN. However, for the workstation to reach the internet, the router must have a default route (0.0.0.0/0) pointing to the ISP's next-hop gateway (likely 203.0.113.6, the other end of the /30 WAN link). Without this route, the router does not know where to forward packets destined for external networks, even though the WAN interface has a valid IP from DHCP.
What should I do if I get this 220-1201 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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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Last reviewed: Jul 4, 2026
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