The Domain Name System (DNS) helps computers find services by name. A website name such as example.com is convenient for people, while network connections need an IP address. DNS provides a way to look up the address associated with a name.
What happens during a lookup?
Your browser asks the operating system to resolve a name. A DNS resolver, often provided by your network or internet service provider, checks whether it already has a recent answer. If not, it can ask other DNS servers until it reaches a server authoritative for that domain. The result is returned to your device, which can then attempt to connect.
The answer may be cached for a limited time to avoid repeating every lookup. DNS records have a time to live value that guides how long an answer may be kept. Changes to a record can therefore take time to appear everywhere.
DNS is only one step
A successful DNS lookup does not prove that a website is working. The server might be unavailable, the connection could be blocked, or the browser could have a separate problem. Likewise, a Wi-Fi connection can be strong while DNS lookups fail. These are different layers of the connection.
A simple diagnostic check
On Windows, nslookup asks a DNS server for a name. Open a terminal and run:
nslookup example.com
This is a read-only lookup; it does not change network settings. If it returns an address but the website still does not load, investigate the connection or website separately. If it reports a lookup failure, compare several names before deciding that one site's DNS is at fault.
When Wi-Fi drops out
If the entire wireless connection repeatedly disconnects, start with Wi-Fi keeps disconnecting. Changing DNS settings will not repair a weak radio signal or a router that is losing power.