DHCP Options Supported by Clients (121005)


The information in this article applies to:

  • Microsoft Windows NT Server 3.5
  • Microsoft Windows NT Server 3.51
  • Microsoft Windows NT Server 4.0
  • Microsoft Windows NT Workstation 3.5
  • Microsoft Windows NT Workstation 3.51
  • Microsoft Windows NT Workstation 4.0
  • Microsoft Windows 95
This article was previously published under Q121005

SUMMARY

Windows NT DHCP (Dynamic Host Configuration Protocol) server service allows a DHCP server to provide a list of options that can be sent to DHCP clients. The options provide configuration information for the DHCP client. Options supported by the DHCP server are defined in RFC 1533, and Microsoft DHCP clients can accept only a few of these options.

MORE INFORMATION

Currently Microsoft DHCP clients can accept and use the following two options: 
   - DHCP Protocol Options
   - Information Options
NOTE: Values in parentheses () are code numbers for each corresponding option.

DHCP Protocol Options

DHCP message type (53): This option is used to convey the type of the DHCP message. The code for this option is 53, and its length is 1. Legal values for this option are: 
   Value   Message Type
   -----   ------------
     1     DHCPDISCOVER
     2     DHCPOFFER
     3     DHCPREQUEST
     4     DHCPDECLINE
     5     DHCPACK
     6     DHCPNAK
     7     DHCPRELEASE
Lease Time (51): This option is used in a client request (DHCPDISCOVER or DHCPREQUEST) to allow the client to request a lease time for the IP address. In a server reply (DHCPOFFER), a DHCP server uses this option to specify the lease time it is willing to offer. The time is in seconds, and is specified as a 32-bit unsigned integer. The code for this option is 51, and its length is 4.

Renewal Time (58): This option specifies the time interval from address assignment until the client transitions to the RENEWING state. The value is in seconds, and is specified as a 32-bit unsigned integer. The code for this option is 58, and its length is 4.

Rebind Time (59): This option specifies the time interval from address assignment until the client transitions to the REBINDING state. The value is in seconds, and is specified as a 32-bit unsigned integer. The code for this option is 59, and its length is 4.

Information Options

Subnet Mask (1): The subnet mask option specifies the client's subnet mask as per RFC 950 [5]. If both the subnet mask and the router option are specified in a DHCP reply, the subnet mask option MUST be first. The code for the subnet mask option is 1, and its length is 4 octets.

Default Router (3): The router option specifies a list of IP addresses for routers on the client's subnet. Routers should be listed in order of preference. The code for the router option is 3. The minimum length for the router option is 4 octets, and the length MUST always be a multiple of 4.

DNS Server (6): The domain name server option specifies a list of Domain Name System (STD 13, RFC 1035 [8]) name servers available to the client. Servers should be listed in order of preference. The code for the domain name server option is 6. The minimum length for this option is 4 octets, and the length must always be a multiple of 4.

Domain Name (15): The Domain Name option specifies the DNS Domain Name that the DHCP Server is to assign the clients for DNS Host name resolution.

WINS Server (NetBIOS Name Server) (44): The NetBIOS name server (NBNS) option specifies a list of RFC 1001/1002 [19] [20] NBNS name servers listed in order of preference. The code for this option is 44. The minimum length of the option is 4 octets, and the length must always be a multiple of 4.

NetBIOS Node Type (46): The NetBIOS node type option allows NetBIOS over TCP/IP clients that are configurable to be configured as described in RFC 1001/1002. The value is specified as a single octet that identifies the client type as follows: 
   Value         Node Type
   -----         ---------
    0x1           B-node
    0x2           P-node
    0x4           M-node
    0x8           H-node
In the above chart, each value indicates a number in base-16 (hexadecimal). The code for this option is 46 and the length is 1.

NetBIOS Scope Id (47): The NetBIOS scope option specifies the NetBIOS over TCP/IP scope parameter for the client as specified in RFC 1001/1002. See codes [19], [20], and [8] for character-set restrictions. The code for this option is 47 and minimum length is 1. Any other options received by the client are ignored and discarded, and are not available through any mechanism. Please note that the NetBIOS Scope ID is case sensitive.

Router Discovery (31) (Windows 2000 or later): check RFC 2132 for more details.

Classless route (249) (Windows XP or later): check the following Web page for more details:

http://www.ietf.org/rfc/rfc3442.txt

Static router(33) (Windows or later): Check RFC 2132 for more details.

NOTE: The DHCP client can change registry settings as defined by rules in:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Dhcp\Parameters\Options\Option ID

Each of these options has corresponding code in the DHCP client that, among others, needs to convert the data before it can be added to the Windows NT registry. Thus, it is not possible to add additional keys here as no data conversion would take place.
Modification Type:MajorLast Reviewed:6/2/2006
Keywords:kbnetwork KB121005
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