When attempting to join a computer to an Active Directory domain, if a pop-up box with message the specified domain either does not exist or could not be contacted appears, first confirm that the domain name being entered is valid. If you have access to the Active Directory Domain Controller, use the PowerShell Get-ADDomain cmdlet to verify the domain name. The client computer should be able to use the name of the forest, which is dc1.software.eng.us in this example.
On the client computer, the nslookup command should be able to resolve the name of the Domain Controller to the IP address of the domain controller. In this example, the nslookup command is able to resolve dc1.software.eng.us to 192.168.0.20. If the nslookup command fails to resolve the name of the Domain Controller to the IP address of the Domain Controller, you will need to check your DNS server. If your DNS server is a Linux BIND DNS server, run the nslookup commands on the BIND DNS server itself.
When attempting to join a computer to an Active Directory domain, there will be a prompt to enter the name of an account with permission to join the domain. This should be a valid Active Directory user account.