Computers with numeric hostname cannot be added manually to the console, but it works if they are searched within the domain.
Following steps explain the steps to reproduce the error or add the computer by searching in Active Directory:
Navigate to Configuration > Computers.
Right-click on Add computers.
Type computer hostname with only numbers in name say, 22222 and click Add. The following error is displayed:
Invalid Computer name or IP
- The computer is correctly added if this is searched within the Active Directory using the From Domain button.
EndPointSecurity 2013 (All builds)
As this Microsoft Knowledge Base states: In Windows 2000 and in later versions of Windows, computers that are members of an Active Directory domain cannot have names that are composed completely of numbers. This restriction is because of DNS restrictions.
Thus it is not possible to add a computer with hostname having only numbers.