Networking / Beginners

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Assigning DHCP Options

DHCP options provide clients with additional configuration data, such as specific server addresses, along with an address lease. For example, when the Transmission Control Protocol/Internet Protocol (TCP/IP) properties of a client computer have been configured to obtain a DNS server address automatically, that computer is relying on DHCP options configured at the DHCP server to acquire a DNS server address (or set of addresses).

You can configure options at the reservation level, scope level, or server level. Options set at the reservation level override all others, and scope-level options override serverlevel options.

To configure options for a reservation, select the particular reservation's icon in the DHCP console tree, and then from the Action or shortcut menu, select Configure Options. To configure options for a scope (after completing the New Scope Wizard), select the Scope Options folder in the DHCP console tree, and then from the Action or shortcut menu, select Configure Options. To configure options for a server, select the Server Options folder in the DHCP console tree, and then from the Action or shortcut menu, select Configure Options. The dialog box that opens after each of these procedures is virtually the same.

More than 60 standard DHCP options are available. The most common of these include the following:

• 003 Router A preferred list of IP addresses for routers on the same subnet as DHCP clients. The client can then contact these routers as needed to forward IP packets destined for remote hosts.
• 006 DNS Servers The IP addresses for DNS name servers that DHCP clients can contact and use to resolve a domain host name query.
• 015 DNS Domain Name An option that specifies the domain name that DHCP clients should use when resolving unqualified names during DNS domain name resolution. This option also allows clients to perform dynamic DNS updates.
• 044 WINS/NBNS Servers The IP addresses of primary and secondary WINS servers for the DHCP client to use.
• 046 WINS/NBT Node Type A preferred NetBIOS name resolution method for the DHCP client to use-such as b-node (0x1) for broadcast only or h-node (0x8) for a hybrid of point-to-point and broadcast methods.
• 051 Lease An option that assigns a special lease duration only to remote access clients. This option relies on user class information advertised by this client type.