Objective
Troubleshoot a situation where a domain is not resolving to a DNS Server.
Prerequisites
None.
Steps
Step 1: Verify if the DNS of a Domain is Responsive via Ping
Launch Command Prompt (cmd) and enter the following command.
ping netonboard.com
If the command sends the following response, it means that the domain could be resolved by the DNS.
Pinging netonboard.com [104.26.0.240] with 32 bytes of data:
Reply from 104.26.0.240: bytes=32 time=32ms TTL=53
Reply from 104.26.0.240: bytes=32 time=32ms TTL=53
Reply from 104.26.0.240: bytes=32 time=32ms TTL=53
Reply from 104.26.0.240: bytes=32 time=32ms TTL=53
Ping statistics for 104.26.0.240:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 32ms, Maximum = 32ms, Average = 32ms
However, if the command sends the following response, it means that the domain could not be resolved by the DNS or you may have entered an invalid domain name.
Ping request could not find host netonboard.com. Please check the name and try again.
Step 2: Verify if the DNS of a Domain is Responsive via nslookup
Launch Command Prompt (cmd) and enter the following command.
ipconfig /all
In the command’s output list, look for the DNS Servers section and take note of the IP address listed.
For this example, the DNS Server that we are using is 8.8.8.8.
Next, run the following command on the command prompt.
nslookup 8.8.8.8 netonboard.com
The command will then start querying the DNS server at 8.8.8.8 for the netonboard.com domain.
If the query is successful, it will show the domain IP address of netonboard.com.
On the other hand, if the query fails, it will state that the command could not find the server address for “netonboard.com“
Step 3: Verify that the DNS port is responsive
Launch Command Prompt (cmd) and enter the following command.
ipconfig /all
In the command’s output list, look for the DNS Servers section and take note of the IP address listed.
For this example, the DNS Server that we are using is 8.8.8.8.
Launch the following command in your command prompt.
The command means that we are performing a telnet to the DNS Server 8.8.8.8 through port 53.
telnet 8.8.8.8 53
If the telnet is successful, you will be redirected to a blank screen.
However, if it fails, the output will state that the command could not find the server address for “netonboard.com”.
Step 4: Restart the DNS Service
For Windows
Launch the the command prompt and enter the following command to restart your DNS.
ipconfig /flushdns
For CentOS
SSH into your CentOS Server as an account that has the necessary permission for these operations (such as root).
On the terminal, enter the following command.
/etc/init.d/dnsmasq restart
Step 5: Verify that the DNS Record is Refreshed
To verify that the record is refreshed, run the following command again.
nslookup netonboard.com