DNS Troubleshooting
Learn how to troubleshoot DNS issues and website resolution failures.
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What Is DNS?
Have you ever visited a website only to see a message saying:
"This site can't be reached"
"Server not found"
If so, DNS may be the reason.
DNS (Domain Name System) works like the internet's phone book. When you type a website address such as google.com into your browser, your device doesn't actually know where that website is located. Instead, it sends a request to a DNS server to find the website's IP address.
Once the IP address is found, your device can connect to the correct server and load the website.
If the DNS server is down, unreachable, or returning incorrect information, your device may be unable to find the website, resulting in errors such as:
This site can't be reached
DNS_PROBE_FINISHED_NXDOMAIN
Server not found
DNS server not responding
In this guide, you'll learn how DNS works, common causes of DNS failures, commands to run during troubleshooting, and how to restore connectivity when DNS issues occur.
Example
Use this section as your baseline before working through the symptoms, commands, and fixes below.
Common Symptoms
DNS issues can appear in several ways. Some of the most common symptoms include:
Websites fail to load even though Wi-Fi is connected
"This site can't be reached" errors
"DNS Server Not Responding" messages
Some websites work while others do not
Slow website loading times
Applications that require internet access fail to connect
New devices can connect to the network but cannot browse the internet
Common Causes
DNS Server Outage:
The DNS server being used may be temporarily unavailable or experiencing issues.
Incorrect DNS Settings:
A device may be configured with an incorrect DNS server address.
ISP DNS Problems:
Internet Service Providers often provide their own DNS servers. If those servers experience issues, websites may become unreachable.
Corrupted DNS Cache:
Your device stores recently visited DNS records in a cache. If that cache becomes outdated or corrupted, it may prevent websites from loading correctly.
Firewall or Security Software:
Certain security applications may block DNS traffic or interfere with DNS lookups.
Commands to Run
Verify DNS Resolution:
Windows, macOS, and Linux:
nslookup google.com
If DNS is working correctly, the command should return an IP address.
Test Internet Connectivity:
ping 8.8.8.8
If the ping succeeds but websites still won't load, DNS may be the issue.
Test Website Resolution:
ping google.com
If the hostname cannot be resolved, DNS is likely failing.
View DNS Configuration:
Windows:
ipconfig /all
Look for:
DNS Servers
Default Gateway
IP Address
Flush DNS Cache:
Windows:
ipconfig /flushdns
macOS:
sudo dscacheutil -flushcache
sudo killall -HUP mDNSResponder
This clears cached DNS records and forces the device to request fresh information.
How to Fix
Restart Your Router:
Many DNS issues can be resolved by restarting the router and modem.
Change DNS Servers:
Try using a public DNS provider:
Cloudflare:
Primary: 1.1.1.1
Secondary: 1.0.0.1
Google:
Primary: 8.8.8.8
Secondary: 8.8.4.4
Flush the DNS Cache:
Clear any outdated records using the commands above.
Verify DNS Settings:
Ensure the device is receiving valid DNS server addresses from the router or DHCP server.
Test Again:
Run:
nslookup google.com
If an IP address is returned, DNS is functioning properly.