My computer is displaying an error message saying it can't find the server address. How do I fix this?

When you enter a website address into your browser and immediately see errors like "Unable to resolve server domain name" or "DNS_PROBE_FINISHED_NXDOMAIN," it means your computer cannot find the corresponding "phone number" (IP address) for that website in its internet "phone book." This problem could stem from your computer's settings, your network connection, or the website's status. Don't panic; we can troubleshoot step-by-step, starting with the most likely cause.

First, consider the simplest possibility: you entered the wrong URL. Carefully check your address bar to see if you've added or omitted any letters, or if the domain suffix (e.g., `.com`, `.cn`) is correct. Next, try accessing other websites. If only this one website is inaccessible, it's likely a problem with that website itself, such as a server outage or expired domain. You can try accessing the same website using mobile data or using a third-party website status checker. If all websites are inaccessible, then the problem lies with you.

The first step is to restart your router and modem. This can resolve many temporary network problems and DNS caching issues. Power off the device, wait one minute, and then power it back on. Test if the network is restored. If the problem persists, we'll begin more in-depth troubleshooting.

The problem might be with your computer's local DNS cache. The operating system caches recently queried domains to speed up access, but sometimes these cached records can be incorrect or expired. Clearing them is a good start.

On a Windows computer, open Command Prompt as administrator and run the command to clear the cache:

ipconfig /flushdns

On macOS, different commands are needed depending on the system version. For newer versions, you can do this:

sudo dscacheutil -flushcache

sudo killall -HUP mDNSResponder

On Linux systems, if you're using the `systemd-resolved` service, you can clear it like this:

sudo systemctl restart systemd-resolved

Sometimes, a special file can interfere with DNS. This file is called `hosts`, and it's like a local-priority private phone book. If the file incorrectly points you to the wrong website or blocks it altogether, it will cause DNS resolution failure. We need to check this file.

On Windows, the file path is `C:\Windows\System32\drivers\etc\hosts`. On Linux or macOS, the path is `/etc/hosts`. Open it with Notepad (Windows) or a text editor (macOS/Linux) and see if there is a line containing the domain name you cannot access. If so, comment it out by adding a `#` symbol at the beginning of the line, or delete the line directly, and then save the file.

# Quickly view the contents of the hosts file on Linux/macOS

cat /etc/hosts

Next, check your DNS server settings. Your computer may be using the DNS server provided by your internet service provider by default, but sometimes these servers are unstable or slow. We can manually switch to a faster and more reliable public DNS server, such as Google's `8.8.8.8` or Cloudflare's `1.1.1.1`.

On Windows, go to Control Panel -> Network and Sharing Center -> click on the currently connected network -> Properties -> select Internet Protocol Version 4 (TCP/IPv4) -> click Properties -> select "Use the following DNS server addresses", and then enter `8.8.8.8` and `8.8.4.4`.

On Linux systems (using the graphical interface of NetworkManager), you can modify the DNS in the network connection settings similarly. If using the command line, you can edit the configuration file (such as `/etc/resolv.conf`, but note that it may be overwritten). A more reliable method is to set it in the Network Manager configuration.

After modifying the DNS, you need to test whether the new settings have taken effect in the command line. Use the `nslookup` (supported by all systems) or `dig` (more commonly used on Linux/macOS) tools to query the domain name resolution status.

# Use nslookup to query, for example, to query baidu.com

nslookup baidu.com

# Use dig to query, which will give more detailed information

dig baidu.com

If these commands return the correct list of IP addresses, the DNS resolution itself is working. If it returns "Server failed" or times out, your current network environment may be completely blocking DNS queries. In this case, you need to check your firewall settings. Some security software or system firewalls may be incorrectly blocking the DNS query port (UDP 53). Try temporarily disabling your firewall or security software to see if the problem is resolved. If so, you need to add an exception for DNS queries in your firewall rules.

Another possibility is that your network is forcibly using a proxy server. If you haven't configured it yourself, it may be a requirement of your company or campus network. Check your system's proxy settings: search for "proxy" in Windows settings, or check it in System Preferences -> Network -> Advanced -> Proxy on macOS. If you don't need a proxy, make sure these settings are turned off.

If after the above steps your computer still cannot resolve any domain names, but your phone connects to the same Wi-Fi normally, the problem may be more complex. Try manually assigning a static IP address to your computer. Sometimes, DHCP automatic IP acquisition might not correctly allocate DNS information. In network settings, besides configuring DNS, you can also try manually specifying the IP address and gateway (usually the gateway is your router's address, such as `192.168.1.1`).

Finally, consider some edge cases. If you are using a business network, DNS queries might be performed through a private network tunnel. Try disconnecting the private network connection to see if you can access the internet directly. If you are using a VPN, check if its patterns or rules are incorrectly blocking or forwarding DNS requests, causing query failures.

For website developers or server administrators, if a large number of users report being unable to resolve your domain name, the problem lies with you. You need to log in to your domain registrar's control panel and check if the DNS records (mainly A records or CNAME records) are correctly pointing to your server's IP address. Also, check if the domain name has expired. You can use online DNS propagation check tools to check your domain name resolution status from around the world to see if DNS updates have not yet been synchronized to all servers globally.

In short, resolving the "unable to resolve server domain name" problem is a troubleshooting process that progresses from local to remote, and from simple to complex issues. Starting with restarting the device and clearing the cache, then checking the hosts file and changing DNS servers, and finally checking firewalls and proxies, most problems can be located and resolved within this process. Remember this order, and the next time you encounter a webpage that won't open, you'll be able to systematically reconnect to the network.