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.
Currently Microsoft DHCP clients can accept and use the following two
- DHCP Protocol Options
- Information Options
: 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
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.
Subnet Mask (1): The subnet mask option specifies the client's subnet
mask as per RFC 950 . 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
DNS Server (6): The domain name server option specifies a list of Domain
Name System (STD 13, RFC 1035 ) 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   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
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
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 , , and  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:
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:
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.