DHCP Options Supported by Clients
This article was previously published under Q121005
This article has been archived. It is offered "as is" and will no longer be updated.
Windows NT DHCP (Dynamic Host Configuration Protocol) server serviceallows a DHCP server to provide a list of options that can be sent to DHCPclients. The options provide configuration information for the DHCPclient. Options supported by the DHCP server are defined in RFC 1533, andMicrosoft DHCP clients can accept only a few of these options.
Currently Microsoft DHCP clients can accept and use the following twooptions:
- DHCP Protocol Options - Information OptionsNOTE: Values in parentheses () are code numbers for each corresponding option.
DHCP Protocol OptionsDHCP message type (53): This option is used to convey the type of theDHCP 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 DHCPRELEASELease Time (51): This option is used in a client request (DHCPDISCOVERor DHCPREQUEST) to allow the client to request a lease time for the IPaddress. In a server reply (DHCPOFFER), a DHCP server uses this optionto 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 is51, and its length is 4.
Renewal Time (58): This option specifies the time interval fromaddress 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 addressassignment until the client transitions to the REBINDING state. Thevalue is in seconds, and is specified as a 32-bit unsigned integer. Thecode for this option is 59, and its length is 4.
Information OptionsSubnet Mask (1): The subnet mask option specifies the client's subnetmask as per RFC 950 . If both the subnet mask and the router optionare 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 addressesfor routers on the client's subnet. Routers should be listed in order ofpreference. The code for the router option is 3. The minimum length forthe router option is 4 octets, and the length MUST always be a multipleof 4.
DNS Server (6): The domain name server option specifies a list of DomainName System (STD 13, RFC 1035 ) name servers available to the client.Servers should be listed in order of preference. The code for the domainname 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 thatthe 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   NBNS name serverslisted in order of preference. The code for this option is 44. The minimumlength of the option is 4 octets, and the length must always be a multipleof 4.
NetBIOS Node Type (46): The NetBIOS node type option allows NetBIOSover TCP/IP clients that are configurable to be configured as describedin RFC 1001/1002. The value is specified as a single octet that identifiesthe client type as follows:
Value Node Type ----- --------- 0x1 B-node 0x2 P-node 0x4 M-node 0x8 H-nodeIn 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 overTCP/IP scope parameter for the client as specified in RFC 1001/1002. Seecodes , , and  for character-set restrictions. The code forthis option is 47 and minimum length is 1. Any other options received bythe client are ignored and discarded, and are not available through anymechanism. 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:
NOTE: The DHCP client can change registry settings as defined by rules in:
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Dhcp\Parameters\Options\Option IDEach 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.
prodnt RFC NBT NetBT
Article ID: 121005 - Last Review: 12/04/2015 10:33:15 - Revision: 4.1
Microsoft Windows NT Server 3.5, Microsoft Windows NT Server 3.51, Microsoft Windows NT Server 4.0 Standard Edition, Microsoft Windows NT Workstation 3.5, Microsoft Windows NT Workstation 3.51, Microsoft Windows NT Workstation 4.0 Developer Edition, Microsoft Windows 95
- kbnosurvey kbarchive kbnetwork KB121005