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.
220-1101 IP Addressing Practice Question
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.
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 reach the router, so the LAN is fine. The router has a WAN IP, but without a default route (or NAT), traffic from the LAN cannot be forwarded to the internet. The /30 WAN subnet only has two usable IPs, so the router needs a route to the ISP's next hop. This tests routing and NAT concepts.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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.
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: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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 220-1201 question in full detail.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related 220-1201 subnetting questions on CIDR, address ranges, and subnet selection.
IP Addressing — This question tests IP Addressing — CIDR notation defines the prefix length..
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 reach the router, so the LAN is fine. The router has a WAN IP, but without a default route (or NAT), traffic from the LAN cannot be forwarded to the internet. The /30 WAN subnet only has two usable IPs, so the router needs a route to the ISP's next hop. This tests routing and NAT concepts.
What should I do if I get this 220-1201 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related 220-1201 subnetting questions on CIDR, address ranges, and subnet selection.
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?
CIDR notation defines the prefix length.
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