Recipe 14.2. Authorizing a DHCP ServerProblemYou want to permit (i.e., authorize) a DHCP Server to process DHCP requests from clients. This is necessary only if the DHCP Server is a member of an Active Directory domain. SolutionUsing a graphical user interface
Using a command-line interfaceThe following command authorizes a DHCP Server in Active Directory: > netsh dhcp add server <DHCPServerName> <DHCPServerIP> This example shows how to authorize the DHCP Server named dhcp01.rallencorp.com with IP 192.168.191.15: > netsh dhcp add server dhcp01.rallencorp.com 192.168.191.15 Using VBScriptSee the Introduction for more information on how to run the netsh command from within a script. The following script prints out the list of authorized DHCP Servers in Active Directory: ' ------ SCRIPT CONFIGURATION ------ strForestRootDN = "<ForestRootDN>" ' e.g., dc=rallencorp,dc=com ' ------ END CONFIGURATION --------- set objCont = GetObject("LDAP://CN=DhcpRoot,CN=NetServices,CN=Services," & _ "CN=Configuration," & strForestRootDN) colDHCPServers = objCont.GetEx("dhcpServers") for each strDHCPServer in colDHCPServers Wscript.Echo strDHCPServer next DiscussionWindows 2000 and Windows Server 2003-based DHCP servers that belong to an Active Directory domain must be authorized before they can give out leases to clients. This feature helps reduce the danger of a rogue Windows 2000 or Windows Server 2003 DHCP Server that an end-user sets up, perhaps unintentionally. A rogue DHCP Server can provide incorrect lease information or deny lease requests altogether, ultimately causing a denial of service for clients on your network. If the DHCP Server service is enabled on a domain controller, it is automatically authorized. A DHCP Server that is a member server of an Active Directory domain performs a query in Active Directory to determine whether it is authorized. If it is, it will respond to DHCP requests; if not, it will not respond to requests. A standalone DHCP server that is not a member of an Active Directory domain sends out a DHCPINFORM message when it first initializes. If an authorized DHCP Server responds to the message, the standalone server will not respond to any further DHCP requests. If it does not receive a response from a DHCP Server, it will respond to client requests and give out leases. DHCP servers are represented in Active Directory as objects of the dhcpClass class, which can be found in the cn=NetServices,cn=Services,cn=Configuratation,<ForestRootDN> container. The relative distinguished name of these objects is the DHCP Server's IP address. There is also an object in the same container named cn=dhcpRoot, which is created after the first DHCP Server is authorized. It has an attribute named dhcpServers that contains all authorized servers. I enumerated this attribute in the VBScript solution to display all authorized servers. By default, only members of the Enterprise Admins group can authorize DHCP Servers. You, however, can delegate the rights to authorize a DHCP Server. Do the following to delegate the necessary permissions to a group called DHCP Admins:
Using a graphical user interfaceYou can quickly determine whether a DHCP Server has been authorized by looking at its server node in the left pane of the DHCP snap-in. If the icon has a little red flag, that means it isn't authorized, if it is green, then it is authorized. Using a command-line interfaceTo see the list of authorized servers using the command line, run the following command: > netsh dhcp show server See AlsoMS KB 279908 (Unexpected Results in the DHCP Service Snap-In After Using NETSH to Authorize DHCP), MS KB 300429 (HOW TO: Install and Configure a DHCP Server in an Active Directory Domain in Windows 2000), and MS KB 303351 (How to Use Netsh.exe to Authorize, Unauthorize, and List DHCP Servers in Active Directory), MS KB 306925 (Cannot Authorize New DHCP Server in Active Directory), and MS KB 323360 (HOW TO: Install and Configure a DHCP Server in an Active Directory Domain in Windows Server 2003) |