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Assigning options

Updated: January 21, 2005

Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2

Assigning options

You can manage DHCP options at several distinct levels:

  • Predefined options.  At this level, you control which types of options are predefined for the DHCP server to expose as available options for assigning from any of the option configuration dialog boxes (such as Server Options, Scope Options, or Reservation Options) available through the DHCP console. You can add or remove options to and from the predefined list of standard options as needed. Although options are made available in this way, they are not assigned values until administratively configured at either the server, scope, or reservation.

  • Server options.  Assign values here (using the General tab) for options that should apply to or be inherited by all scopes and clients of the DHCP server as defaults. Options configured here can have their values overridden by different values if those values are set at either a scope, options class, or reserved client level.

  • Scope options.  Assign values here (using the General tab) for options that should apply only to clients of an applicable scope selected in the DHCP console tree. Options configured here can have their values overridden by different values if those values are set at either an options class or reserved client level.

  • Reservation options.   Assign values for options that should apply only to a specific reserved DHCP client. To use this level of assignment, you must first add a reservation for the applicable client to the applicable DHCP server and scope where the client is to obtain its IP address. These options are set for an individual DHCP client configured with an address reservation in a scope. Only properties manually configured at the client computer can override options assigned at this level.

  • Class options.  When using any of the option configuration dialog boxes (Server Options, Scope Options or Reservation Options), you can click the Advanced tab to configure and enable options for assignment to identifying member clients of a specified user or vendor class.

    Depending on the context, only those DHCP clients that identify themselves according to the selected class are distributed options data you have configured specifically for that class. For example, if a class-assigned option is set at a scope, only clients of that scope that indicate class membership during leasing activity are configured with class-assigned option values. Other non-member clients are configured using scope option values set from the General tab.

    Options configured here can override values assigned and set at the same context (either server, scope, or reservation options) or values inherited from options configured at a higher context. However, the ability of the client to indicate membership in a specific options class is typically the decisive criteria for using this level of options assignment. For more information, see Using option classes.

Guidelines for assigning options

The following guidelines can help you determine what level to assign the options you use for clients on your network.

  • Add or define new custom option types only if you have new software or applications that require a nonstandard DHCP option.

  • If your DHCP server manages many scopes for a large network, be selective when assigning Server Options. These options apply by default to all clients of a DHCP server computer, unless otherwise overridden.

  • Use Scope Options for assigning most options that clients use. In most networks, this level is typically preferred for assigning and enabling the use of DHCP options.

  • Use Class Options if you have a mixture of DHCP clients with diverse needs that are able to identify a specific class on the DHCP server when obtaining a lease. For example, if you have a limited number of DHCP client computers running Windows 2000, these clients can be configured to receive vendor-specific options that other clients do not use.

  • Use Reservation Options for individual DHCP clients in your network that have special configuration requirements.

    For any hosts (that is, computers or other networked devices) that do not support DHCP or are not recommended to use it, you can also consider excluding IP addresses for those computers and devices and manually setting the IP address configuration directly at the applicable host. For example, you often need to statically configure the IP address for routers.

Commonly used options

After you set basic TCP/IP configuration settings (such as IP address, subnet mask, and default gateway) for clients, most clients also need the DHCP server to provide other information through DHCP options. The most common of these include the following:

  • Routers.  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.

  • DNS servers.  IP addresses for DNS name servers that DHCP clients can contact and use to resolve a domain host name query.

  • DNS domain.  Specifies the domain name that DHCP clients should use when resolving unqualified names during DNS domain name resolution.

  • WINS node type.  A preferred NetBIOS name resolution method for the DHCP client to use (such as b-node for broadcast only or h-node for a hybrid of point-to-point and broadcast methods).

  • WINS server.  IP addresses of primary and secondary WINS servers for the DHCP client to use.

Note

  • When the DHCP service is installed, no DHCP option definitions are created. Option definitions are created only when the DHCP console is opened for the first time. If you want to configure the value of an option on a DHCP server on which the console has never been opened, you must first use the Netsh DHCP context command server add optiondef (at a netsh dhcp> command prompt or in a batch file or script) to create the option definition. To use Netsh to assign a value to the option definition you have created, use the Netsh DHCP context command server set optionvalue. For more information, see Netsh commands for DHCP.

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