Domain Question

I work at a medium sized company doing assistant network administration.

When setting up a computer I join the PC to the domain.

Basic stuff give it a name and join it.

However every so often it wont except the domain name. So ill enter in [DomainName] and it will tell me its not recognized. So ill enter [DomainName].com and it will allow me to connect. I find that windows 7 machines prefer the .com suffix.

Thats fine I understand enough about naming to get why it would ask for a .com. But occasionally Ill get an issue from a user about not being able to log into the domain. I go in and the computer has attached itself to the [DomainName].com address I have to drop the .com and log back into the domain.

Can anyone explain the difference between a [DomainName] and a [DomainName].com?

Or the reasons why a computer that's connected to the domain will all of the sudden attach a .com?

You're having DNS Suffix issues. A quick assumption would be that your DNS configuration is being applied by a GPO. The GPO is getting applied to the computer and working correctly. When the GPO hasn't applied, isn't applied, or possibly has a different GPO based on the scope, it may be causing some other issues.

For example, you want to join your domain and just type 'domain' in there. DNS may append the required suffix to create domain.com. In the case that you are typing domain.com, it may want to ad another suffix, domain.com.com which would cause an issue.

Overall, you want to view the DNS entries on the system that is exhibiting the issue and determine if those settings are correct. This is assuming you have verified the basics such as network connectivity, able to ping, etc.

You can easily verify DNS is working by using the NSLOOKUP tool or by pinging the name of a server or computer. The results in the ping response will respond with the FQDN of the system. If it does not, DNS is not configured properly.