Adding Domain Controllers by Using #DOM

The #DOM keyword can be used in LMHOSTS files to distinguish a Windows NT domain controller from other computers on the network. To use the #DOM tag, follow the name and IP address mapping in LMHOSTS with the #DOM keyword, a colon, and the domain in which the domain controller participates. For example:

102.54.94.97     primary        #PRE    #DOM:mydomain    #The mydomain PDC

Using the #DOM keyword to designate domain controllers adds entries to a domain name cache that is used to contact available controllers for processing domain requests. When domain controller activity such as a logon request occurs, the request is sent to the domain group name. On the local subnet, the request is broadcast and is picked up by any local domain controllers. However, if you use the #DOM keyword to specify domain controllers in the LMHOSTS file, Microsoft TCP/IP uses datagrams to also forward the request to domain controllers located on remote subnets. Adding more domain controllers in the LMHOSTS file will help distribute the load on all the controllers.

The following list contains guidelines for mapping important members of the domain by using the #DOM keyword.

• It is recommended that the #DOM entries be pre-cached by using the #PRE keyword. Note that the #PRE keyword must precede the #DOM keyword.

• For each local LMHOSTS file on a Windows NT computer that is a member in a domain, there should be #DOM entries for all domain controllers in the domain that are located on remote subnets. This ensures that logon authentication, password changes, browsing, and so on, all work properly for the local domain. These are the necessary minimum entries.

• For local LMHOSTS files on all servers that can be backup domain controllers, there should be mappings for the primary domain controller's name and IP address, plus mappings for all other backup domain controllers. This ensures that promoting a backup to primary domain controller status does not affect the ability to offer all services to members of the domain.

• If trust relationships exist between domains, all domain controllers for all trusted domains should also be listed in the local LMHOSTS file.

• For domains that you want to browse from your local domain, the local LMHOSTS files should contain at least the name and IP address mapping for the primary domain controller in the remote domain. Again, backup domain controllers should also be included so that promotion to primary domain controller does not impair the ability to browse remote domains.

Names that appear with the #DOM keyword in the LMHOSTS file are placed in a special domain name list in NetBT. When a datagram is sent to this domain using the DOMAIN<1C> name, the name is resolved first by using WINS or IP broadcasts. The datagram is then sent to all the addresses contained in the list from LMHOSTS, and there is also a broadcast on the local subnet.