How to determine if it's a DNS issue or a server issue? A practical troubleshooting guide

　　In daily website maintenance or network usage, we often encounter problems like "webpages can't be opened," "server response timeout," and "DNS resolution failure." Many users' first reaction to these situations is that the server is down. However, not all access failures are caused by the server itself. Often, the real cause lies with the DNS (Domain Name System). Accurately determining whether the issue lies with the DNS or the server allows for quicker troubleshooting and resolution.

　　To determine the root cause of a problem, you must first understand the relationship between DNS and servers in network access. When a user enters a URL (such as www.example.com), the system first requests resolution from a DNS server, converting the domain name into an IP address. Only after the IP address is returned can the browser establish a connection with the target server and load the webpage. Therefore, the access process can be divided into two phases: the DNS resolution phase and the server response phase. The DNS phase is responsible for finding the target address, while the server phase is responsible for providing the content. If access fails, it's important to determine whether the address cannot be found or the address has been found but the browser is unable to access the website.

　　When you suspect a website is inaccessible, the simplest initial diagnosis is to use the ping command. Open a command prompt (type CMD on Windows, open Terminal on macOS and Linux) and enter:

ping www.example.com

　　If the command output displays "Ping request could not find host" or "Unknown host," the system cannot resolve the domain name, likely due to a DNS issue. If the IP address can be resolved but "Request timed out" or "Unable to reach target host" appears, DNS resolution is normal and the problem lies with the server or network link.

　　For further verification, use the nslookup command, a tool specifically designed for querying DNS resolution results. Enter:

nslookup www.example.com

　　If the command returns one or more IP addresses, DNS resolution is working properly. If it displays "Non-existent domain" or the returned IP address is clearly incorrect (for example, pointing to an intranet address), this indicates a DNS anomaly. You can try changing the DNS server, such as changing the system DNS to Google DNS (8.8.8.8) or Cloudflare DNS (1.1.1.1), and retest. If the website is accessible after the change, it confirms that the issue is with DNS resolution, not a server malfunction.

　　In addition to system commands, you can also use online tools such as "dnschecker.org" or "whatsmydns.net" to verify domain name resolution consistency across different nodes globally. If resolution works in some regions but not others, it suggests that the DNS record may not have fully taken effect or there may be a caching issue. If resolution fails on all nodes, it's likely that the domain's DNS configuration is incorrect or the record has been deleted.

　　On the other hand, if DNS resolution is working but the website still doesn't open, you need to verify the server's health. First, you can verify network connectivity by pinging the IP address. For example, if pinging www.example.com fails, but pinging its corresponding IP address works, the problem lies with DNS resolution. If both fail, the server may be offline, a firewall may be blocking ICMP requests, or the network link may be faulty.

　　For more precise diagnosis, use the tracert (Windows) or traceroute (Linux/macOS) command to view the packet's path.

tracert www.example.com

　　This command displays every network node from the local device to the target server. If all requests time out after a specific node, the problem lies with the network routing after that node. If you can successfully reach the target IP address but still can't open the webpage, check whether the server port is open or the website service is functioning properly.

　　Sometimes the server is online, but the website is still inaccessible. This may be due to a problem with the server's services (such as HTTP, HTTPS, FTP, etc.). You can use the telnet command to check whether the port connection is functioning properly. For example:

telnet www.example.com 80

　　If a connection failure message appears, it means the web service port is blocked by a firewall or the service is not started. For HTTPS websites, try port 443. If telnet can connect but the webpage still won't load, the problem may lie in the website's application layer, such as a program crash, database connection failure, or configuration error.

　　Another common way to diagnose the problem is to use a third-party network monitoring service. For example, visit "DownForEveryoneOrJustMe.com" or "IsItDownRightNow.com" and enter the target website address. If the global detection shows "Down" across all services, it's almost certain that the server is experiencing a problem. If the problem persists only locally but not elsewhere, the problem is likely related to DNS or the local network cache.

　　From a system perspective, DNS issues typically have the following characteristics:

• Only specific websites are inaccessible, while other websites function normally;
• Accessing the page using the IP address works;
• The problem disappears after changing the DNS server or clearing the cache;
• Access results vary on different devices or networks.

　　Server issues manifest as:

• No users can access the website;
• The IP address cannot be pinged or the port is refusing connections;
• The service is slow to respond, with frequent timeouts or 502 or 504 errors;
• The website backend, control panel, or database are unavailable.

　　For average users, if you're unable to determine the source of the problem, start with simple troubleshooting steps. First, clear the local DNS cache (run ipconfig /flushdns on Windows), then restart your browser and router and try accessing the website again. If that still doesn't work, try switching DNS servers. If you still can't access the website, use the Ping and Nslookup commands to check the results. If the domain name resolution is normal but the website doesn't open, it's almost certain that there's a problem at the server or network level.