DNS, or Domain Name System, is a vital component of the internet infrastructure, translating user-friendly domain names into machine-readable IP addresses. When DNS fails, websites, email, and other online services become unreachable. Signs You're Dealing With a DNS Problem DNS issues usually show up as errors like "This site can't be reached," DNS_PROBE_FINISHED_NXDOMAIN, "Server DNS address could not be found," or a browser that hangs on "Resolving host..." before timing out. A good way to tell DNS apart from a broader connectivity problem: if you can reach a site by typing its raw IP address but not its domain name, DNS is almost always the cause. Step 1: Confirm It's Actually DNS Before changing any settings, run a quick lookup to see whether your computer can resolve domain names at all. Windows: Open Command Prompt and run nslookup itms-us.com. If it returns an IP address, DNS resolution is working; if it times out or errors, DNS is likely the problem. macOS: Open Terminal and run the same command, nslookup itms-us.com. Step-by-Step DNS Troubleshooting Check TCP/IP Settings: Confirm your computer uses the correct DNS servers in the network settings (see the Windows and macOS instructions below). Flush DNS Cache: Clear any outdated DNS records. Open Command Prompt as administrator and run: ipconfig /flushdns On macOS, open Terminal and run: sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder Release and Renew DHCP Lease: Reset network configuration to get new DNS addresses. In an elevated Command Prompt, run: ipconfig /release ipconfig /renew Use Different DNS Servers: If issues persist, switch to a public DNS provider: Google Public DNS: 8.8.8.8 and 8.8.4.4 Cloudflare DNS: 1.1.1.1 and 1.0.0.1 Changing DNS Servers on Windows Open Control Panel > Network and Internet > Network and Sharing Center > Change adapter settings. Right-click your connection > Properties > Internet Protocol Version 4 (TCP/IPv4) > Properties. Select "Use the following DNS server addresses" and enter your preferred and alternate DNS addresses, then click OK. Changing DNS Servers on macOS Open System Settings (System Preferences on macOS Monterey and earlier) > Network > select your connection > Details > DNS. Click "+" to add your new DNS server addresses and click OK, then Apply. Changing DNS Servers on Mobile iOS: Settings > Wi-Fi > tap the "i" next to your network > Configure DNS > Manual > add the server addresses. Android: Settings > Network & Internet > Internet > tap your network's gear icon > Private DNS > enter a provider hostname (e.g., dns.google or 1dot1dot1dot1.cloudflare-dns.com). Verify the Fix Worked After applying any of the steps above, re-run nslookup itms-us.com (or try loading a few different websites) to confirm name resolution has been restored before moving on to the next step. Additional Tips If the problem persists after these steps, check whether a VPN or third-party security software is overriding your DNS settings, restart your router and devices, and confirm any custom DNS configurations on your router itself are correct. If you suspect the issue is on your provider's end, contact your ISP directly. DNS problems can also be a symptom of larger network issues. If you're still stuck after working through this guide, our Remote Computer Support and Network Services teams can diagnose and resolve it for you. You may also find our guide on Port Numbers and Sockets Explained useful for understanding how network traffic flows alongside DNS.