Two background services make modern networks usable: DHCP, which gives devices an address automatically, and DNS, which turns human-friendly names into the addresses devices actually use. When either fails, the symptoms are distinctive and easy to diagnose once you understand them.
DHCP: Automatic Addressing
DHCP (Dynamic Host Configuration Protocol) is the service that automatically gives a device the settings it needs to communicate: an IP address, the default gateway, and which DNS servers to use. Without it, every device would have to be configured by hand.
- A device joins the network and requests configuration.
- The DHCP server assigns an available address and the supporting settings.
- The device can now communicate, no manual setup required.
When DHCP fails: a device gets no valid address and cannot communicate normally at all, the symptom is "no network," not "names do not work."
DNS: Names to Addresses
DNS (Domain Name System) translates names people can remember into the numerical addresses networks use. People type a name; DNS resolves it to an address; the device connects to that address.
When DNS fails: the device has a valid address and can reach other devices by address, but cannot reach anything by name. This very specific symptom, "addresses work, names do not", is the signature of a DNS problem.
Telling Them Apart
| Symptom |
Likely service |
| Device has no valid address at all |
DHCP |
| Address works, local devices reachable, but names fail |
DNS |
| Everything works by address but every website name fails |
DNS |
| Device cannot communicate on the network at all |
DHCP or the link |
This pair is one of the most testable troubleshooting distinctions in the course: no address points to DHCP; names-only failure points to DNS.
Practice Questions
A device has a valid IP address and can reach other local devices, but cannot open any website by name. Which service is the MOST likely culprit?
- A. DHCP, because the device has no address
- B. DNS, because names are not resolving to addresses
- C. The firewall, because traffic is blocked entirely
- D. The power supply, because the device is on
Answer: B. A valid address and local reachability rule out DHCP and the link. Failure only when using names is the classic DNS signature.
A newly connected device cannot communicate on the network at all and shows no valid address. Which service is MOST likely involved?
- A. DNS, because names are failing
- B. DHCP, because the device did not receive an address
- C. QoS, because traffic is not prioritized
- D. Port forwarding, because no path is open
Answer: B. No valid address at all points to DHCP (or the underlying link), not DNS. DNS problems show up only when using names, after a valid address is in place.
Frequently Asked Questions
What is the difference between DNS and DHCP?
DHCP automatically assigns a device its address and settings; DNS translates names into addresses. They solve different problems and fail with different symptoms.
What happens when DNS fails?
The device has a valid address and can reach others by address, but cannot reach anything by name, the signature names-only failure.
What happens when DHCP fails?
The device gets no valid address and cannot communicate on the network normally at all, a no-network symptom rather than a names-only one.