The tables in this section describe the predefined options available for configuration of DHCP clients. These options are defined in RFC 1533.
You can use Microsoft DHCP Server to set any of the options described in this section. Microsoft DHCP clients however, support only the options whose code and option name are listed in bold type. If you have third-party DHCP clients, you can set any option listed that is supported by the third-party client software.
Table 13.1 Basic Options
Code | Option name | Meaning |
0 | Pad | Causes subsequent fields to align on word boundaries. |
255 | End | Indicates end of options in the DHCP packet. |
1 | Subnet mask | Specifies the subnet mask of the client subnet. This option is defined in the Create Scope or Scope Properties dialog box. It cannot be set directly in an Option dialog box. |
2 | Time offset | Specifies the Universal Coordinated Time (UCT) offset in seconds. |
3 | Router | Specifies a list of IP addresses for routers on the client's subnet.1 |
4 | Time server | Specifies a list of IP addresses for time servers available to the client.1 |
5 | Name servers | Specifies a list of IP addresses for name servers available to the client.1 |
6 | DNS servers | Specifies a list of IP addresses for DNS name servers available to the client.1 Multihomed computers can have only one list per computer, not one per adapter card. |
7 | Log servers | Specifies a list of IP addresses for MIT_LCS User Datagram Protocol (UDP) log servers available to the client.1 |
8 | Cookie servers | Specifies a list of IP addresses for RFC 865 cookie servers available to the client.1 |
9 | LPR servers | Specifies a list of IP addresses for RFC 1179 line-printer servers available to the client.1 |
10 | Impress servers | Specifies a list of IP addresses for Imagen Impress servers available to the client.1 |
11 | Resource location servers | Specifies a list of RFC 887 Resource Location servers available to the client.1 |
12 | Host name | Specifies the host name of up to 63 characters for the client. The name must start with a letter, end with a letter or digit, and have as interior characters only letters, numbers, and hyphens. The name can be qualified with the local DNS domain name. |
13 | Boot file size | Specifies the size of the default boot image file for the client, in 512-octet blocks. |
14 | Merit dump file | Specifies the ASCII path name of a file where the client's core image is dumped if a crash occurs. |
15 | Domain name | Specifies the DNS domain name the client should use for DNS host name resolution. |
16 | Swap server | Specifies the IP address of the client's swap server. |
17 | Root path | Specifies the ASCII path name for the client's root disk. |
18 | Extensions path | Specifies a file retrievable via TFTP containing information interpreted the same as the vendor-extension field in the BOOTP response, except the file length is unconstrained and references to Tag 18 in the file are ignored. |
1 List is specified in order of preference.
The following table lists IP layer parameters on a per-host basis.
Table 13.2 IP Layer Parameters per Host
Code | Option name | Meaning |
19 | IP layer forwarding | Enables or disables forwarding of IP packet for this client. 1 enables forwarding; 0 disables it. |
20 | Nonlocal source routing | Enables or disables forwarding of datagrams with nonlocal source routes. 1 enables forwarding; 0 disables it. |
21 | Policy filter masks | Specifies policy filters that consist of a list of pairs of IP addresses and masks specifying destination/mask pairs for filtering nonlocal source routes. Any source routed datagram whose next-hop address does not match a filter will be discarded by the client. |
22 | Max DG reassembly size | Specifies the maximum size datagram that the client can reassemble. The minimum value is 576. |
23 | Default time-to-live | Specifies the default time-to-live (TTL) that the client uses on outgoing datagrams. The value for the octet is a number between 1 and 255. |
24 | Path MTU aging timeout | Specifies the timeout in seconds for aging Path Maximum Transmission Unit (MTU) values (discovered by the mechanism defined in RFC 1191). |
25 | Path MTU plateau table | Specifies a table of MTU sizes to use when performing Path MTU Discovered as defined in RFC 1191. The table is sorted by size from smallest to largest. The minimum MTU value is 68. |
The following table lists IP parameters on a per-interface basis. These options affect the operation of the IP layer on a per-interface basis. A client can issue multiple requests, one per interface, to configure interfaces with their specific parameters.
Table 13.3 IP Parameters per Interface
Code | Option name | Meaning |
26 | MTU option | Specifies the MTU discovery size for this interface. The minimum MTU value is 68. |
27 | All subnets are local | Specifies whether the client assumes that all subnets of the client's internetwork use the same MTU as the local subnet where the client is connected. 1 indicates that all subnets share the same MTU; 0 indicates that the client should assume some subnets might have smaller MTUs. |
28 | Broadcast address | Specifies the broadcast address used on the client's subnet. |
29 | Perform mask discovery | Specifies whether the client should use Internet Control Message Protocol (ICMP) for subnet mask discovery. 1 indicates the client should perform mask discovery; 0 indicates the client should not. |
30 | Mask supplier | Specifies whether the client should respond to subnet mask requests using ICMP. 1 indicates the client should respond; 0 indicates the client should not respond. |
31 | Perform router discovery | Specifies whether the client should solicit routers using the router discovery method in RFC 1256. 1 indicates that the client should perform router discovery; 0 indicates that the client should not use it. |
32 | Router solicitation address | Specifies the IP address to which the client submits router solicitation requests. |
33 | Static route | Specifies a list of IP address pairs that indicate the static routes the client should install in its routing cache. Any multiple routes to the same destination are listed in descending order or priority. The routes are destination/router address pairs. (The default route of 0.0.0.0 is an illegal destination for a static route.) |
The following table lists link layer parameters per interface. These options affect the operation of the data link layer on a per-interface basis.
Table 13.4 Link Layer Parameters per Interface
Code | Option name | Meaning |
34 | Trailer encapsulation | Specifies whether the client should negotiate use of trailers (RFC 983) when using the ARP protocol. 1 indicates the client should attempt to use trailer; 0 indicates the client should not use trailers. |
35 | ARP cache timeout | Specifies the timeout in seconds for ARP cache entries. |
36 | Ethernet encapsulation | Specifies whether the client should use Ethernet v. 2 (RFC 894) or IEEE 802.3 (RFC 1042) encapsulation if the interface is Ethernet. 1 indicates that the client should use RFC 1042 encapsulation; 0 indicates the client should use RFC 894 encapsulation. |
The following table shows TCP parameters. These options affect the operation of the TCP layer on a per-interface basis.
Table 13.5 TCP Parameters
Code | Option name | Meaning |
37 | Default time-to-live | Specifies the default TTL the client should use when sending TCP segments. The minimum value of the octet is 1. |
38 | Keepalive interval | Specifies the interval in seconds the client TCP should wait before sending a keepalive message on a TCP connection. A value of 0 indicates that the client should not send keepalive messages on connections unless specifically requested by an application. |
39 | Keepalive garbage | Specifies whether the client should send TCP keepalive messages with an octet of garbage data for compatibility with older implementations. 1 indicates that a garbage octet should be sent; 0 indicates that it should not be sent. |
The following table shows application layer parameters. These miscellaneous options are used to configure applications and services.
Table 13.6 Application Layer Parameters
Code | Option name | Meaning |
40 | NIS domain name | Specifies the name of the Network Information Service (NIS) domain as an ASCII string. |
41 | NIS servers | Specifies a list of IP addresses for NIS servers available to the client.1 |
42 | NTP servers | Specifies a list of IP addresses for Network Time Protocol (NTP) servers available to the client.1 |
1 List is specified in order of preference.
The following options are for vendor-specific information.
Table 13.7 Vendor-Specific Information
Code | Option name | Meaning |
43 | Vendor specific info | Binary information used by clients and servers to exchange vendor-specific information. Servers not equipped to interpret the information ignore it. Clients that don't receive the information attempt to operate without it. |
Table 13.8 NetBIOS Over TCP/IP
Code | Option name | Meaning |
44 | WINS/NBNS servers | Specifies a list of IP addresses for NetBIOS name servers (NBNS).1 |
45 | NetBIOS over TCP/IP NBDD | Specifies a list of IP addresses for NetBIOS datagram distribution servers (NBDD).1 |
46 | WINS/NBT node type | Allows configurable NetBIOS over TCP/IP clients to be configured as described in RFC 1001/1002, where 1=b-node, 2=p-node, 4=m-node, and 8=h-node. On multihomed computers, the node type is assigned to the entire computer, not to individual adapter cards. |
47 | NetBIOS scope ID | Specifies as a string that is the NetBIOS over TCP/IP Scope ID for the client, as specified in RFC 1001/1002. On multihomed computers, the scope ID is assigned to the entire computer, not to individual adapter cards. |
48 | X Window system font | Specifies a list of IP addresses for X Window font servers available to the client.1 |
49 | X Window system display | Specifies a list of IP addresses for X Window System Display Manager servers available to the client.1 |
1 List is specified in order of preference.
Table 13.9 DHCP Extensions
Code | Option name | Meaning |
51 | Lease time | Specifies the time in seconds from address assignment until the client's lease on the address expires. Lease time is specified in the Create Scope or Scope Properties dialog box. It cannot be set directly in a DHCP Options dialog box. |
58 | Renewal (T1) time value | Specifies the time in seconds from address assignment until the client enters the renewing state. Renewal time is a function of the lease time option, which is specified in the Create Scope or Scope Properties dialog box. It cannot be set directly in a DHCP Options dialog box. |
59 | Rebinding (T2) time value | Specifies the time in seconds from address assignment until the client enters the rebinding state. Rebinding time is a function of the lease time option, which is specified in the Create Scope or Scope Properties dialog box. It cannot be set directly in a DHCP Options dialog box. |