How to join a domain in windows 7?

Before joining the Windows 7 computer to a domain, make sure you understand the following requirements:

Using Windows 7 Professional, Ultimate or Enterprise - Windows 7 only these editions can join a domain. No, Windows 7 Home cannot. Do not try.

Having a network interface card (NIC) - Of course, but unless you have one (or a wireless connection), how do you expect to connect to the server?

Being physically connected to the LAN - Windows 7 (and earlier operating systems) is an auto-sensing LAN. Every time you disconnect from the network, a balloon appears in the tray notifying you of the disconnected state. Note that Windows 7 can be joined in an offline mode to a domain in Windows Server 2008 R2.

Have a valid IP address - Valid for the network you are connected. You can be manually configured, you receive one from a DHCP server or leave it alone and you get an APIPA address (which begins with 169.254.xy). If it is an APIPA address you are asking potential problems such as APIPA and AD do not go together hand in hand.

Provide all-time connectivity to the domain controller - or at least one of them. The IP address has been configured (or leased) should be enough for you to connect to one of domain controllers in your domain. You can test your connectivity with ping, but note that aping was successful does not guarantee that you have good connection with the distribution centers.