How to check the proxy firewall and DNS configuration?

To check your proxy, firewall, and DNS configuration, inspect each layer in turn:

• Proxy: Run netsh winhttp show proxy on Windows, scutil --proxy on macOS, or env | grep -i proxy on Linux.
• Firewall: Review Windows Defender Firewall, the macOS firewall, or sudo ufw status.
• DNS: Run ipconfig /all (Windows) or nslookup/dig to verify resolution, then flush the cache if needed.

The same phrase is also Chrome's suggestion text on connectivity errors such as ERR_CONNECTION_TIMED_OUT and ERR_PROXY_CONNECTION_FAILED.

What "Check your proxy, firewall, and DNS configuration" means

That exact sentence is the suggestion Chrome appends to "This site can't be reached" when it cannot establish a connection. You will see it next to error codes such as ERR_CONNECTION_TIMED_OUT, ERR_PROXY_CONNECTION_FAILED, ERR_NETWORK_CHANGED, and ERR_CONNECTION_REFUSED. Chrome is pointing you at the three network layers that most often break a request before it ever reaches the destination server.

Each layer plays a distinct role. A proxy is an intermediary that can reroute or block traffic; a misconfigured or offline proxy stops requests cold. A firewall enforces allow and deny rules; an over-aggressive rule can silently drop the connection. DNS translates a hostname into an IP address; if resolution fails, the browser never learns where to connect. Checking the configuration means verifying that none of these three is interfering.

How to check your proxy configuration

On Windows

• Open Settings > Network & Internet > Proxy and check the Automatically detect settings and Use a proxy server toggles.
• For the legacy view, run inetcpl.cpl to open Internet Properties, go to the Connections tab, and click LAN settings.
• From the command line, run netsh winhttp show proxy to view the system-wide WinHTTP proxy.

On macOS

• Open System Settings > Network, select your active interface, then Details > Proxies.
• From Terminal, run scutil --proxy for the resolved proxy state, or networksetup -getwebproxy "Wi-Fi" for the HTTP proxy on a named service.

On Linux and the command line

• Run env | grep -i proxy to list the http_proxy, https_proxy, and no_proxy environment variables.
• On GNOME, check Settings > Network > Network Proxy; also inspect /etc/environment and package-manager configs such as /etc/apt/apt.conf.d/ for system proxies.
• In Chrome itself, visit chrome://settings/system and click Open your computer's proxy settings; Chrome defers to the OS proxy.
• To confirm a proxy connection is genuinely in use, run netstat -an and look for the proxy host and port among the established connections.

How to check your firewall configuration

• Windows: open Control Panel > Windows Defender Firewall and review Allow an app through firewall, or run netsh advfirewall show allprofiles from an elevated prompt to see whether your app or port is blocked.
• macOS: open System Settings > Network > Firewall to toggle it and set per-app rules under Options, or run sudo /usr/libexec/ApplicationFirewall/socketfilterfw --getglobalstate to read the current state.
• Linux: run sudo ufw status verbose on Ubuntu/UFW, sudo firewall-cmd --list-all on firewalld systems, or sudo iptables -L -n to view raw rules.
• Third-party suites: remember that antivirus and security products (Norton, McAfee, Kaspersky) often bundle their own firewall, which can block traffic even when the OS firewall looks fine.

How to check your DNS configuration

• Windows: run ipconfig /all to see the configured DNS servers, then test resolution with nslookup testmu ai.com. The GUI lives under the adapter's IPv4 properties.
• macOS: view your resolver with scutil --dns or cat /etc/resolv.conf, and test with dig testmu ai.com or nslookup.
• Linux: run resolvectl status (systemd-resolved) or cat /etc/resolv.conf, then test with dig, host, or nslookup.
• Reading the output: a healthy lookup returns an A record with an IP address and TTL. A "server can't find" or NXDOMAIN response means resolution failed, which points the blame at DNS rather than the proxy or firewall.

How to fix the "Check your proxy, firewall, and DNS configuration" error

• Rule out the obvious first: Reload the page, try a different site, and restart your router to confirm the problem is local.
• Disable or verify the proxy: Turn off "Use a proxy server", uncheck the LAN proxy, and disconnect any VPN that might be rerouting traffic.
• Check the firewall and antivirus: Temporarily disable them to test, then re-enable and add an allow rule for the app rather than leaving protection off.
• Flush the DNS cache: Windows: ipconfig /flushdns. macOS: sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder. Linux: sudo resolvectl flush-caches.
• Renew the connection (Windows): Run ipconfig /release then ipconfig /renew, followed by netsh winsock reset and netsh int ip reset, then reboot.
• Switch to public DNS: Use Google 8.8.8.8 / 8.8.4.4 or Cloudflare 1.1.1.1 / 1.0.0.1 in your adapter's DNS settings.
• Clean up Chrome: Clear the browser cache, disable extensions, try Incognito, and check the hosts file for stale entries.
• Flush Chrome's internal DNS: Visit chrome://net-internals/#dns and click Clear host cache.

Proxy, firewall, and DNS in cloud and automation testing

Network configuration matters even more when you test applications that are not publicly exposed. Staging environments, locally hosted builds, and apps behind a corporate firewall are unreachable from cloud browsers unless you bridge the gap. This is where TestMu AI Tunnel comes in, opening a secure connection so cloud browsers and real devices can reach your private or local environment (see Testing Locally Hosted Pages).

For the tunnel to connect, your proxy, firewall, and DNS must allow it. In restricted networks you typically configure the tunnel binary with the proxy host, port, and credentials, supply custom DNS servers where required, and whitelist the TestMu AI domains and IP ranges in your firewall. Getting these three layers right locally is exactly what keeps a cloud testing session from failing with the same proxy, firewall, and DNS symptoms you would see in a browser.

Troubleshooting cheat-sheet

• Proxy: Windows netsh winhttp show proxy | macOS scutil --proxy | Linux env | grep -i proxy | active connection netstat -an.
• Firewall: Windows netsh advfirewall show allprofiles | macOS socketfilterfw --getglobalstate | Linux sudo ufw status verbose / sudo iptables -L -n.
• DNS view: Windows ipconfig /all | macOS scutil --dns | Linux resolvectl status.
• DNS test: nslookup (all platforms) or dig (macOS/Linux); look for an A record versus a "can't find" error.
• DNS flush: Windows ipconfig /flushdns | macOS sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder | Linux sudo resolvectl flush-caches.
• Error mapping: ERR_PROXY_CONNECTION_FAILED points to the proxy, ERR_CONNECTION_REFUSED often to the firewall or server, and ERR_NAME_NOT_RESOLVED to DNS, while ERR_CONNECTION_TIMED_OUT can stem from any of the three.

Frequently Asked Questions

How do I check if a proxy server is running on my computer?

Run netsh winhttp show proxy on Windows, scutil --proxy on macOS, or env | grep -i proxy on Linux to see the configured proxy. To confirm a proxy connection is actually active, run netstat -an and look for the proxy host and port in the list of established connections.

How do I fix "Check your proxy, firewall, and DNS configuration"?

Disable or verify your proxy and VPN, test with the firewall or antivirus temporarily off and then re-enable it with an allow rule, flush the DNS cache with ipconfig /flushdns (or the macOS/Linux equivalent), renew your IP, switch to a public DNS such as 8.8.8.8 or 1.1.1.1, and clear Chrome's cache or try Incognito. Work through these in order until the page loads.

What does ERR_CONNECTION_TIMED_OUT mean and how is it related?

It means Chrome could not reach the server within the allotted time. Because a stale proxy, a blocking firewall, or a failed DNS lookup are common causes, Chrome shows the "Check your proxy, firewall, and DNS configuration" suggestion alongside this error and related ones such as ERR_PROXY_CONNECTION_FAILED and ERR_NETWORK_CHANGED.

How do I flush DNS on Windows, macOS, and Linux?

On Windows run ipconfig /flushdns. On macOS run sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder. On modern Linux with systemd-resolved run sudo resolvectl flush-caches (or sudo systemd-resolve --flush-caches on older systems).

Should I change my DNS to 8.8.8.8 or 1.1.1.1?

Switching to a public resolver helps when your ISP's DNS is slow or failing. Google Public DNS uses 8.8.8.8 and 8.8.4.4, while Cloudflare uses 1.1.1.1 and 1.0.0.1. Set these in your network adapter's IPv4 DNS settings, then flush the cache so the new resolver takes effect immediately.

How do I check my firewall settings?

On Windows open Windows Defender Firewall or run netsh advfirewall show allprofiles. On macOS open System Settings > Network > Firewall or run sudo /usr/libexec/ApplicationFirewall/socketfilterfw --getglobalstate. On Linux run sudo ufw status verbose, sudo firewall-cmd --list-all, or sudo iptables -L -n depending on your firewall.

• How to Check Proxy Settings?
• What Are Proxy Settings?
• How to Turn Off Proxy?
• What Is a HTTP Proxy?