CompTIA A+ Core 1 (220-1201)Hardware and Network TroubleshootingHard
A user reports that their desktop computer's internet connection is extremely slow, but locally they can access other devices on the network at normal speeds. When they try to browse websites, pages load very slowly or time out. Pinging local IP addresses works fine, but pinging external websites by domain name fails. Pinging external websites by IP address works. What is the MOST likely cause?
- AFaulty Network Interface Card (NIC).
- BISP uplink congestion.
- CIncorrect DNS server configuration.
- DOverloaded local network switch.
Show answer & explanationAnswer & explanation
Correct answer: C. Incorrect DNS server configuration.
The ability to ping local devices and external IP addresses, but not external domain names, is a classic symptom of a DNS (Domain Name System) resolution failure. The computer cannot translate website names into their corresponding IP addresses, preventing web browsing, even if the underlying internet connection is otherwise functional.
Why the other options are wrong
- A. A faulty NIC would typically affect all network traffic, local and external, by IP or domain name.
- B. ISP uplink congestion would affect both pinging external IPs and domain names, and would not explain why local network access is normal.
- D. An overloaded local switch would affect local network speeds as well as internet access, which contradicts the 'local access normal' symptom.
DNS Resolution Failure
A network problem where a computer cannot translate human-readable domain names (e.g., google.com) into numerical IP addresses.
- Prevents web browsing and access to resources by name.
- Ping to IP addresses often works, while ping to domain names fails.
- Caused by incorrect DNS server settings, faulty DNS server, or firewall blocking DNS traffic.
Memory trick: If you know the 'address' but not the 'name', DNS is the one to blame.