A common exam scenario is this: a user can reach a server or website by IP address, but not by host name. That pattern makes DNS a strong suspect, but it does not prove DNS is the only problem. Name resolution can fail because of local settings, a bad DNS server, a blocked query, a stale cache, or a proxy or firewall rule that affects normal browsing even when raw IP tests succeed.
What the symptom really tells you
If a client can ping or connect to a known IP, basic Layer 3 connectivity is present between that client and that destination. The next question is what changes when the user types a name instead of an IP. The system now has to resolve the name into an address before it can connect. If that lookup fails, the application may report that the site cannot be found even though the path to the network is otherwise working.
That is why DNS is often the best first answer on an exam question with this wording. Still, read carefully for caveats. A browser might fail on names because it is using a proxy setting that is wrong, while a direct IP test bypasses that behavior. A firewall might allow one test tool but block DNS traffic. For extra review, use the Networking and Hardware & Network Troubleshooting items in these CompTIA A+ practice questions and focus on explanations that compare likely causes.
Study example: narrow the cause
Study example: A workstation opens http://198.51.100.20 in a browser, but https://intranet.local fails with “server not found.” Another PC on the same switch reaches intranet.local normally.
Useful reasoning:
- Local IP connectivity exists, because the known address opens.
- The remote service is up, because another PC can reach it by name.
- The problem is likely local to the failing workstation.
- DNS settings, DNS cache, hosts file entries, or proxy configuration are better suspects than a switch failure.
A good next check would be whether the failing PC has the correct DNS server configured and whether it can resolve the host name at all. If resolution fails locally while other systems resolve it, the issue is probably not a full network outage.
Practice question with explained answer
Which issue is the best initial diagnosis when a user can reach a web server by IP address but cannot reach it by FQDN, while other users can reach the same FQDN?
- A: Failed DNS resolution on the local client
- B: Complete loss of Internet connectivity
- C: Defective switch port causing no network path
- D: Server power failure
Correct answer: A.
Reasoning: Reaching the server by IP shows that the network path is working at least well enough for that connection. Other users reaching the same FQDN makes a total server outage unlikely. A bad switch port would be less consistent with successful IP connectivity. DNS is the strongest first diagnosis because the failure appears when a name must be translated to an address. However, keep the caveat in mind: DNS is suspect, not guaranteed. Local proxy settings, local firewall rules, or cached incorrect records can create a similar symptom pattern.
For a compact refresher before more questions, the CompTIA A+ cheat sheet is a useful broad review resource, and its PDF download link makes it easy to mark the difference between “best first suspect” and “proven root cause.” On exam items, that distinction often separates a strong answer from an overconfident one.
Official exam reference: CompTIA A+ certification information. These study examples are independently written.