DNS and DHCP often appear together in troubleshooting scenarios, but they fail in different ways. A device with a valid IP address can still fail to reach resources by name if DNS lookup is broken. A device with no valid lease may fail much earlier, before name resolution matters at all. For exam study, focus on what facts separate those patterns.
Pattern 1: Valid address, bad lookup
Study example: A laptop joins the office Wi-Fi and receives an IPv4 address, subnet mask, default gateway, and DNS server. The user says, “I can open a site by typing its IP address, but the name does not work.” That detail points away from DHCP as the primary problem. The host already has a lease, so the more likely issue is DNS resolution.
Cautious next steps:
- Confirm the client really has a valid address and gateway.
- Compare access by IP address versus hostname.
- Check whether the configured DNS server is reachable.
- Try another known hostname to see whether the problem is one name or name resolution generally.
When you want more scenarios like this, use relevant items from the public bank of CompTIA Network+ practice questions and sort your notes into “addressing problem” versus “lookup problem.” That habit makes answer choices easier to eliminate.
Pattern 2: Missing lease
Study example: A desktop is connected to the LAN, but it shows an address that does not match the local network plan, and it cannot reach the gateway. In this case, hostname testing is not the first concern. The host likely did not obtain a proper lease, so DHCP is the earlier failure point.
A careful response is to verify link status, check whether the correct VLAN or SSID is being used, and confirm that the client can reach the DHCP path. If the device never received a valid lease, DNS symptoms may appear later, but they are secondary.
A broader review resource such as the CompTIA Network+ study guide can help you connect these clues with the underlying service roles: DHCP provides addressing information, while DNS translates names to addresses.
Mini diagnostic question with explained answer
A user reports: “I can ping the default gateway. I can also reach the company web server by entering its IP address in the browser. But when I enter the server name, it fails.” Which issue is the best match?
- A: DHCP failed to assign an IP lease
- B: DNS resolution failed
- C: The switch port is down
- D: The subnet mask is missing
Correct answer: B: DNS resolution failed.
Explanation: The client can reach the gateway, so local Layer 3 connectivity exists. The client can also access the server by IP address, which shows network communication to that destination is working. The failure occurs only when using the hostname, which is the clearest sign that name resolution is the problem. Choice A is weaker because the device already has working network settings. Choice C is inconsistent with successful gateway communication. Choice D is unlikely because missing or incorrect mask information would usually break local communication patterns, not only hostname lookups.
For quick review, ask yourself one exam-day question first: does the device already have usable addressing? If yes, suspect DNS when names fail but IP access works. If no, investigate DHCP and connectivity to the lease process before chasing lookup errors.
Official exam reference: CompTIA Network+ certification information. These study examples are independently written.