How To • DNS Troubleshooting • Network Diagnostics

How to troubleshoot DNS when all devices fail

This guide helps you identify and fix DNS (Domain Name System) problems affecting your entire network. You'll learn how to confirm a DNS failure, isolate the cause, and restore internet access for all connected devices.

Note: Steps may vary by device and router model. This guide focuses on safe, general methods.

Quick Answer

Restart your modem and router by unplugging them for 60 seconds.
Try using a public DNS server (like 8.8.8.8) on one computer to test.
Check your router's admin page for DNS settings and reset them to default or a public DNS.
Disable any active VPN or parental control software on your devices temporarily.
Flush the DNS cache on a Windows PC or macOS computer.

If this doesn't work, follow the diagnostic flow and step-by-step guide below.

What you need

Before you start

At least one device connected to your network (Wi-Fi or Ethernet).
Your router's admin login details (often on a sticker on the router).
A computer (Windows, macOS, or Linux) for running diagnostic commands.
Basic knowledge of how to open a command line or terminal.
Physical access to your modem and router.

Good to know

The IP address of a public DNS server (e.g., 8.8.8.8 for Google DNS).
Whether you have any VPN, security suite, or custom DNS software installed.
Your Internet Service Provider's (ISP) support contact information.
The difference between a modem and a router (if you have separate devices).
That changing router settings can temporarily disconnect devices.

Diagnose the issue in 2 minutes

1. Is it only one device or all devices? If all devices fail, the problem is likely at the router or ISP level.
2. Can you ping an IP address but not a website name?
- Open a command line and type: ping 8.8.8.8. If this works...
- Then type: ping google.com. If this fails, it's likely a DNS issue.
3. Is the problem on Wi-Fi, Ethernet, or both? Test with a wired connection if possible. If Ethernet works but Wi-Fi doesn't, the problem may be router Wi-Fi settings, not DNS.
4. Is a VPN or security software active? Temporarily disable them on one device. If internet returns, the software's DNS settings are likely the cause.
5. Did you recently change router settings? A misconfigured DNS entry in the router will affect all devices.

Step-by-step guide

Step 1 — Power cycle your network hardware

This clears temporary glitches in the modem and router.

Unplug the power cables from your modem and router.
Wait 60 seconds.
Plug in the modem first, wait for all its lights to stabilize.
Then plug in the router and wait for it to fully boot.

What you should see: Devices should reconnect. Test if websites load.

Step 2 — Test with a public DNS on one computer

This bypasses your router or ISP's DNS to confirm the problem.

Windows: Go to Network & Internet Settings > Change adapter options > right-click your connection > Properties > TCP/IPv4 > Use "8.8.8.8" and "8.8.4.4".

macOS: System Settings > Network > your connection > Details > DNS. Add "8.8.8.8".

Linux: Edit /etc/resolv.conf (temporary) or use nmcli/nmtui to set DNS to "8.8.8.8".

What you should see: If websites load now, your usual DNS servers are faulty.

Step 3 — Check and update router DNS settings

The router provides DNS to all devices. Incorrect settings here cause widespread failure.

Log into your router's admin page (usually via 192.168.1.1 or 192.168.0.1 in a browser).
Navigate to Internet or WAN settings.
Find the DNS server fields. Set them to "Obtain automatically from ISP" or manually use "8.8.8.8" and "1.1.1.1".
Save settings and reboot the router.

What you should see: After the reboot, all devices should resolve websites correctly.

Step 4 — Flush local DNS cache on devices

Devices store old DNS data that can become corrupted.

Windows: Open Command Prompt as admin, run ipconfig /flushdns.

macOS: Open Terminal, run sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder.

Linux: Depends on service; for systemd-resolved, run sudo systemctl restart systemd-resolved.

What you should see: Clears old entries, forcing the device to request fresh DNS data.

Step 5 — Inspect for software conflicts

Security software, VPNs, or "optimizers" can override system DNS.

Temporarily disable VPN connections on all devices.
Check security suite settings for "DNS protection" or "safe browsing" features; disable to test.
Look for any recently installed network-related applications.

What you should see: If disabling a specific software fixes it, reconfigure or replace that software.

Step 6 — Verify ISP or upstream outage

Sometimes the problem is with your ISP's DNS servers.

Use your phone on cellular data to check your ISP's status page or outage reports.
Contact your ISP's support and ask if there are known DNS server issues.
If using ISP DNS, consider permanently switching to a public DNS like Google (8.8.8.8) or Cloudflare (1.1.1.1).

What you should see: ISP may confirm an outage, providing an expected resolution time.

Common fixes by symptom

Connected but no internet (websites timeout)

Likely causes:

Router's DNS settings are incorrect.
ISP DNS servers are down.
DNS requests are being blocked by firewall.

Safe fixes:

Change router DNS to public servers (8.8.8.8, 1.1.1.1).
Power cycle modem/router.
Temporarily disable router firewall to test.

When to stop and escalate: If changing DNS on the router doesn't help, contact ISP.

Some websites don't open, others work fine

Likely causes:

DNS cache poisoning or corruption.
Specific domain's DNS records are problematic.
Content filtering or parental controls blocking sites.

Safe fixes:

Flush DNS cache on multiple devices.
Try a different public DNS provider.
Check router for any active access controls.

When to stop and escalate: If the problem persists across multiple DNS providers, it may be a host-level issue.

Intermittent "DNS Server Not Responding" errors

Likely causes:

Unstable connection to the DNS server.
Router overheating or hardware flakiness.
ISP connection dropping packets.

Safe fixes:

Ensure router is cool and well-ventilated.
Use a wired connection to rule out Wi-Fi instability.
Test with a reliable DNS server and monitor for timeouts.

When to stop and escalate: If errors continue on a wired connection with a public DNS, suspect router hardware failure.

VPN breaks internet for all other devices

Likely causes:

VPN software on a computer is acting as a DNS sinkhole.
Router's DNS is being forcibly redirected by the VPN.

Safe fixes:

Disconnect the VPN on the device using it.
Check VPN settings to disable "kill switch" or "DNS leak protection" temporarily.
Restart router after disabling VPN.

When to stop and escalate: If you need the VPN active, consult the VPN provider's support for network configuration.

Quick reference

Table A: What the metric means

Metric	Ideal Range	What it tells you about DNS
Latency (Ping to DNS)	< 50 ms	How quickly your DNS server responds. High latency slows down the first step of browsing.
Jitter	< 30 ms	Variation in DNS response times. High jitter can cause inconsistent website loading.
Packet Loss	0%	Lost DNS queries mean timeouts and "server not found" errors.
Throughput	Not a direct DNS metric	DNS uses minimal bandwidth. Slow throughput after DNS resolves is a separate issue.
Signal Strength (Wi-Fi)	> -67 dBm	Weak signal can cause DNS request packets to drop, mimicking a DNS failure.

Table B: Safe baseline settings

Setting	Recommended Baseline	Notes for DNS
Wi-Fi Security	WPA2/WPA3 Personal	Weak security can allow DNS hijacking on your local network.
DNS Servers	ISP Default or 8.8.8.8 / 1.1.1.1	Using two different providers (primary/secondary) adds redundancy.
Router Admin	Change default password	Prevents unauthorized changes to your DNS settings.
Guest Network	Enable if needed, with separate password	Isolates guest devices, but they still use the router's DNS.
Firmware Updates	Check every 6 months	Updates often fix DNS-related bugs and security holes.

Mind map summary

All Devices Have DNS Failure?
├── Diagnosis
│   ├── Ping IP (8.8.8.8) works? → Yes = DNS Problem.
│   └── Ping hostname (google.com) fails? → Yes = DNS Problem.
├── Quick Remedies
│   ├── Power Cycle Modem & Router
│   ├── Test with Public DNS on one PC
│   └── Flush Local DNS Cache
├── Router-Level Fixes
│   ├── Log in, check WAN DNS settings
│   ├── Change to Public DNS (8.8.8.8, 1.1.1.1)
│   └── Reboot router after saving
├── Software Conflicts
│   ├── Disable VPN on all devices
│   └── Check Security Suite DNS settings
└── External Causes
    ├── Check ISP for DNS outage
    └── Consider permanent switch to reliable Public DNS

Troubleshooting checklist

Device

Flush DNS cache.
Disable VPN/security software.
Test with manual public DNS.
Try a different browser.

Router

Power cycle (modem first, then router).
Verify DNS settings in admin panel.
Update firmware if available.
Check for active parental controls.
Disable custom firewall rules temporarily.

ISP & External

Check for known outages.
Test with a different DNS provider.
Contact ISP support.
Ensure modem is online (solid lights).

When to escalate

Contacting ISP: When all devices fail with multiple public DNS servers, and your modem shows no connection lights or reports a downstream/upstream problem. Also, if there's a known area outage.
Replacing router: When DNS failures are intermittent and coincide with router overheating or random disconnects, and a factory reset doesn't solve the problem.
Asking IT support: If you are in a managed office environment, or if the network uses static IPs and complex firewall rules you cannot modify.

What to collect before escalating:

Results from ping tests to an IP and a hostname.
The exact error messages from browsers (e.g., "DNS_PROBE_FINISHED_BAD_CONFIG").
Timestamps of when the problem started and if it's constant or intermittent.
Whether the issue persists on a wired connection.
Your router model and firmware version.

FAQ

What is DNS and why does it fail for all devices at once?

DNS translates website names (like google.com) into IP addresses. If all devices fail at once, the common point of failure is usually your router (which provides DNS to devices) or your ISP's DNS servers. A misconfiguration or outage at this shared level affects everything on your network.

Is it safe to use public DNS servers like Google DNS or Cloudflare DNS?

Yes, in most cases. Public DNS servers are generally reliable, fast, and secure. They can also provide additional features like phishing protection. However, some ISP services (like parental controls or local content filtering) may rely on their own DNS, so switching might bypass those features.

Why does restarting the router fix DNS issues so often?

Routers have temporary memory (cache) that can become corrupted. A restart clears this cache, renews the connection to your ISP, and re-initializes all network services, including the DNS forwarder that hands out addresses to your devices.

Can a virus or malware cause DNS problems for my whole network?

Yes, but it's less common. Malware on a single device can change that device's DNS settings. To affect the whole network, it would need to compromise your router's admin password and change settings there. Ensure your router uses a strong admin password and keep its firmware updated.

My phone works on cellular data but not Wi-Fi. Is this a DNS problem?

It's a strong indicator. If your phone can access the internet via mobile data but not via your home Wi-Fi, the problem is in your local network. Since DNS is a core service for Wi-Fi internet access, it's a likely culprit. Follow the steps to test and change your router's DNS.

What's the difference between "DNS Server Not Responding" and "No Internet Access"?

"DNS Server Not Responding" means your device cannot reach the server that translates names to IPs. "No Internet Access" is broader and means your device has no functional path to the internet at all, which could be due to DHCP, IP, or physical connection failures. DNS failure often feels like "no internet" because browsers can't load sites.

Should I set DNS on my router or on each individual device?

For most home users, setting DNS on the router is easiest as it automatically applies to all devices. Setting it on individual devices is useful for testing or if you need specific devices to use different DNS (e.g., for streaming geo-restricted content).

How can I prevent DNS problems in the future?

Use reliable public DNS servers, keep your router firmware updated, avoid clicking on suspicious links that could install malware, and periodically restart your networking equipment. Consider setting up a secondary DNS server for redundancy.

Sources and references

Microsoft Windows networking documentation (ping, ipconfig, DNS flush commands)
Apple macOS support articles (network diagnostics, DNS configuration)
Linux manual pages (resolv.conf, systemd-resolved, nmcli)
General router administration and setup guides from major manufacturers
Internet Engineering Task Force (IETF) RFCs on DNS concepts and operations
Wi-Fi Alliance and IEEE 802.11 standards overviews
Cybersecurity best practices for home networks (DNS security)
Public DNS provider documentation (Google Public DNS, Cloudflare 1.1.1.1)

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How to troubleshoot DNS when all devices fail

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