DHCP options lookup

 

Dynamic Host Configuration Protocol (DHCP) has many configuration options that can be sent to the clients when they request information from the DHCP server. You can use a lookup tool to see all of the DHCP options.

DHCP options define additional configuration data that the DHCP server passes along to clients in addition to an IP address. Typical options include subnet mask, domain name, router IP addresses, domain name server IP addresses, and static routes.

Standard DHCP options, based on definitions in RFC 2132: DHCP Options and BOOTP Vendor Extensions, are described in the following table. You might also configure customized options using the DHCP Options display in iSeries™ Navigator.

Table 1. Standard DHCP options

Option number	Option	Description
1	Subnet mask	The subnet mask option specifies the client's subnet mask as per Request for Comments (RFC) 950. If both the subnet mask and the router option are specified in a DHCP reply, the subnet mask option must be specified first. The code for the subnet mask option is 1, and its length is 4 octets.
2	Time offset	The time offset field specifies the offset of the client's subnet in seconds from Coordinated Universal Time (UTC). The offset is expressed as a two's complement 32-bit integer. A positive offset indicates a location east of the zero meridian and a negative offset indicates a location west of the zero meridian. The code for the time offset option is 2, and its length is 4 octets.
3	Router	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.
4	Time server	The time server option specifies a list of RFC 868 time servers available to the client. Servers should be listed in order of preference. The code for the time server option is 4. The minimum length for this option is 4 octets, and the length must always be a multiple of 4.
5	Name server	The name server option specifies a list of IEN 116 name servers available to the client. Servers should be listed in order of preference. The code for the name server option is 5. The minimum length for this option is 4 octets, and the length must always be a multiple of 4.
6	Domain Name Server	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.
7	Log server	The log server option specifies a list of MIT-LCS UDP log servers available to the client. Servers should be listed in order of preference. The code for the log server option is 7. The minimum length for this option is 4 octets, and the length must always be a multiple of 4.
8	Cookie server	The cookie server option specifies a list of RFC 865 cookie servers available to the client. Servers should be listed in order of preference. The code for the cookie server option is 8. The minimum length for this option is 4 octets, and the length must always be a multiple of 4.
9	LPR server	The LPR server option specifies a list of RFC 1179 line printer servers available to the client. Servers should be listed in order of preference. The code for the LPR server option is 9. The minimum length for this option is 4 octets, and the length must always be a multiple of 4.
10	Impress server	The Impress server option specifies a list of Imagen Impress servers available to the client. Servers should be listed in order of preference. The code for the Impress server option is 10. The minimum length for this option is 4 octets, and the length must always be a multiple of 4.
11	Resource location server	This option specifies a list of RFC 887 Resource Location servers available to the client. Servers should be listed in order of preference. The code for this option is 11. The minimum length for this option is 4 octets, and the length must always be a multiple of 4.
12	Host name	This option specifies the name of the client. The name might or might not be qualified with the local domain name (see section 3.17 for the preferred way to retrieve the domain name). See RFC 1035 for character set restrictions. The code for this option is 12, and its minimum length is 1.
13	Boot file size	This option specifies the length in 512-octet blocks of the default boot image for the client. The file length is specified as an unsigned 16-bit integer. The code for this option is 13, and its length is 2.
14	Merit dump file	This option specifies the path-name of a file to which the client's core image should be dumped in the event the client crashes. The path is formatted as a character string consisting of characters from the NVT ASCII character set. The code for this option is 14. Its minimum length is 1.
15	Domain name	This option specifies the domain name that client should use when resolving hostnames through the Domain Name System. The code for this option is 15. Its minimum length is 1.
16	Swap server	This specifies the IP address of the client's swap server. The code for this option is 16, and its length is 4.
17	Root path	This option specifies the path-name that contains the client's root disk. The path is formatted as a character string consisting of characters from the NVT ASCII character set. The code for this option is 17. Its minimum length is 1.
18	Extensions path	A string to specify a file, retrievable via TFTP, which contains information that can be interpreted in the same way as the 64-octet vendor-extension field within the BOOTP response, with the following exceptions: The length of the file is unconstrained All references to Tag 18 (that is, instances of the BOOTP Extensions Path field) within the file are ignored. The code for this option is 18. Its minimum length is 1.
19	IP forwarding	This option specifies whether the client should configure its IP layer for packet forwarding. A value of 0 means disable IP forwarding, and a value of 1 means enable IP forwarding. The code for this option is 19, and its length is 1.
20	Non-Local source routing	This option specifies whether the client should configure its IP layer to allow forwarding of datagrams with non-local source routes. A value of 0 means disallow forwarding of such datagrams, and a value of 1 means allow forwarding. The code for this option is 20, and its length is 1.
21	Policy filter	This option specifies policy filters for non-local source routing. The filters consist of a list of IP addresses and masks which specify destination/mask pairs with which to filter incoming source routes. Any source routed datagram whose next-hop address does not match one of the filters should be discarded by the client. The code for this option is 21. The minimum length of this option is 8, and the length must be a multiple of 8.
22	Maximum datagram reassembly size	This option specifies the maximum size datagram that the client should be prepared to reassemble. The size is specified as a 16-bit unsigned integer. The minimum value legal value is 576. The code for this option is 22, and its length is 2.
23	Default IP time to live	This option specifies the default time-to-live that the client should use on outgoing datagrams. The TTL is specified as an octet with a value between 1 and 255. The code for this option is 23, and its length is 1.
24	Path MTU aging timeout	This option specifies the timeout (in seconds) to use when aging Path MTU values discovered by the mechanism defined in RFC 1191. The timeout is specified as a 32-bit unsigned integer. The code for this option is 24, and its length is 4.
25	Path MTU plateau table	This option specifies a table of MTU sizes to use when performing Path MTU Discovery as defined in RFC 1191. The table is formatted as a list of 16-bit unsigned integers, ordered from smallest to largest. The minimum MTU value cannot be smaller than 68. The code for this option is 25. Its minimum length is 2, and the length must be a multiple of 2.
26	Interface MTU	This option specifies the MTU to use on this interface. The MTU is specified as a 16-bit unsigned integer. The minimum legal value for the MTU is 68. The code for this option is 26, and its length is 2.
27	All subnets are local	This option specifies whether the client can assume that all subnets of the IP network to which the client is connected use the same MTU as the subnet of that network to which the client is directly connected. A value of 1 indicates that all subnets share the same MTU. A value of 0 means that the client should assume that some subnets of the directly connected network might have smaller MTUs. The code for this option is 27, and its length is 1.
28	Broadcast address	This option specifies the broadcast address in use on the client's subnet. Legal values for broadcast addresses are specified in section 3.2.1.3 of RFC 2132. The code for this option is 28, and its length is 4.
29	Perform mask discovery	This option specifies whether the client should perform subnet mask discovery using ICMP. A value of 0 indicates that the client should not perform mask discovery. A value of 1 means that the client should perform mask discovery. The code for this option is 29, and its length is 1.
30	Mask supplier	This option specifies whether the client should respond to subnet mask requests using ICMP. A value of 0 indicates that the client should not respond. A value of 1 means that the client should respond. The code for this option is 30, and its length is 1.
31	Perform router discovery	This option specifies whether the client should solicit routers using the Router Discovery mechanism defined in RFC 1256. A value of 0 indicates that the client should not perform router discovery. A value of 1 means that the client should perform router discovery. The code for this option is 31, and its length is 1.
32	Router solicitation address option	This option specifies the address to which the client should transmit router solicitation requests. The code for this option is 32, and its length is 4.
33	Static route	This option specifies a list of static routes that the client should install in its routing cache. If multiple routes to the same destination are specified, they are listed in descending order of priority. The routes consist of a list of IP address pairs. The first address is the destination address, and the second address is the router for the destination. The default route (0.0.0.0) is an illegal destination for a static route. The code for this option is 33. The minimum length of this option is 8, and the length must be a multiple of 8.
34	Trailer encapsulation	This option specifies whether the client should negotiate the use of trailers (RFC 893) when using the ARP protocol. A value of 0 indicates that the client should not attempt to use trailers. A value of 1 means that the client should attempt to use trailers. The code for this option is 34, and its length is 1.
35	ARP cache timeout	This option specifies the timeout in seconds for ARP cache entries. The time is specified as a 32-bit unsigned integer. The code for this option is 35, and its length is 4.
36	Ethernet encapsulation	This option specifies whether the client should use Ethernet Version 2 (RFC 894) or IEEE 802.3 (RFC 1042) encapsulation if the interface is an Ethernet. A value of 0 indicates that the client should use RFC 894 encapsulation. A value of 1 means that the client should use RFC 1042 encapsulation. The code for this option is 36, and its length is 1.
37	TCP default TTL	This option specifies the default TTL that the client should use when sending TCP segments. The value is represented as an 8-bit unsigned integer. The minimum value is 1. The code for this option is 37, and its length is 1.
38	TCP keep-alive interval	This option specifies the interval (in seconds) that the client TCP should wait before sending a keepalive message on a TCP connection. The time is specified as a 32-bit unsigned integer. A value of zero indicates that the client should not generate keepalive messages on connections unless specifically requested by an application. The code for this option is 38, and its length is 4.
39	TCP keep-alive garbage	This option specifies whether the client should send TCP keepalive messages with an octet of garbage for compatibility with older implementations. A value of 0 indicates that a garbage octet should not be sent. A value of 1 indicates that a garbage octet should be sent. The code for this option is 39, and its length is 1.
40	Network information service domain	This option specifies the name of the client's NIS domain. The domain is formatted as a character string consisting of characters from the NVT ASCII character set. The code for this option is 40. Its minimum length is 1.
41	Network information servers	This option specifies a list of IP addresses indicating NIS servers available to the client. Servers should be listed in order of preference. The code for this option is 41. Its minimum length is 4, and the length must be a multiple of 4.
42	Network time protocol servers option	This option specifies a list of IP addresses indicating NTP servers available to the client. Servers should be listed in order of preference. The code for this option is 42. Its minimum length is 4, and the length must be a multiple of 4.
44	NetBIOS over TCP/IP name server	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 of 4.
45	NetBIOS over TCP/IP datagram distribution server	The NetBIOS datagram distribution server (NBDD) option specifies a list of RFC 1001/1002 NBDD servers listed in order of preference. The code for this option is 45. The minimum length of the option is 4 octets, and the length must always be a multiple of 4.
46	NetBIOS over TCP/IP node type	The NetBIOS node type option allows NetBIOS over TCP/IP clients which are configurable to be configured as described in RFC 1001/1002. The value is specified as a single octet which identifies the client type as follows: In the above chart, the notation '0x' indicates a number in base-16 (hexadecimal). The code for this option is 46. The length of this option is always 1.
47	NetBIOS over TCP/IP scope	The NetBIOS scope option specifies the NetBIOS over TCP/IP scope parameter for the client as specified in RFC 1001/1002. The code for this option is 47. The minimum length of this option is 1.
48	X Window System Font server	This option specifies a list of X Window System Font servers available to the client. Servers should be listed in order of preference. The code for this option is 48. The minimum length of this option is 4 octets, and the length must be a multiple of 4.
49	X Window System display manager	This option specifies a list of IP addresses of systems that are running the X Window System Display Manager and are available to the client. Addresses should be listed in order of preference. The code for the this option is 49. The minimum length of this option is 4, and the length must be a multiple of 4.
51	IP address lease time	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 units of seconds, and is specified as a 32-bit unsigned integer. The code for this option is 51, and its length is 4.
58	Renewal (T1) time value	This option specifies the time interval from address assignment until the client transitions to the RENEWING state. The value is in units of seconds, and is specified as a 32-bit unsigned integer. The code for this option is 58, and its length is 4.
59	Rebinding (T2) time value	This option specifies the time interval from address assignment until the client transitions to the REBINDING state. The value is in units of seconds, and is specified as a 32-bit unsigned integer. The code for this option is 59, and its length is 4.
62	NetWare/IP domain name	Specifies the Netware/IP domain name.
63	NetWare/IP	Specifies the NetWare sub-options you want. The range is 1 to 255. Use option 62 to specify the NetWare/IP domain name.
64	NIS domain name	This option specifies the name of the client's NIS+ domain. The domain is formatted as a character string consisting of characters from the NVT ASCII character set. The code for this option is 64. Its minimum length is 1.
65	NIS servers	This option specifies a list of IP addresses indicating NIS+ servers available to the client. Servers should be listed in order of preference. The code for this option is 65. Its minimum length is 4, and the length must be a multiple of 4.
66	Server name	This option is used to identify a TFTP server when the 'sname' field in the DHCP header has been used for DHCP options. The code for this option is 66, and its minimum length is 1.
67	Boot file name	This option is used to identify a bootfile when the 'file' field in the DHCP header has been used for DHCP options. The code for this option is 67, and its minimum length is 1.
68	Home address	This option specifies a list of IP addresses indicating mobile IP home agents available to the client. Agents should be listed in order of preference. The code for this option is 68. Its minimum length is 0 (indicating no home agents are available) and the length must be a multiple of 4. It is expected that the usual length will be four octets, containing a single home agent's address.
69	SMTP servers	The SMTP server option specifies a list of SMTP servers available to the client. Servers should be listed in order of preference. The code for the SMTP server option is 69. The minimum length for this option is 4 octets, and the length must always be a multiple of 4.
70	POP3 server	The POP3 server option specifies a list of POP3 available to the client. Servers should be listed in order of preference. The code for the POP3 server option is 70. The minimum length for this option is 4 octets, and the length must always be a multiple of 4.
71	NNTP server	The NNTP server option specifies a list of NNTP available to the client. Servers should be listed in order of preference. The code for the NNTP server option is 71. The minimum length for this option is 4 octets, and the length must always be a multiple of 4.
72	WWW server	The WWW server option specifies a list of WWW available to the client. Servers should be listed in order of preference. The code for the WWW server option is 72. The minimum length for this option is 4 octets, and the length must always be a multiple of 4.
73	Finger server	The Finger server option specifies a list of Finger available to the client. Servers should be listed in order of preference. The code for the Finger server option is 73. The minimum length for this option is 4 octets, and the length must always be a multiple of 4.
74	IRC server	The IRC server option specifies a list of IRC available to the client. Servers should be listed in order of preference. The code for the IRC server option is 74. The minimum length for this option is 4 octets, and the length must always be a multiple of 4.
75	StreetTalk server	The StreetTalk server option specifies a list of StreetTalk servers available to the client. Servers should be listed in order of preference. The code for the StreetTalk server option is 75. The minimum length for this option is 4 octets, and the length must always be a multiple of 4.
76	STDA server	The StreetTalk Directory Assistance (STDA) server option specifies a list of STDA servers available to the client. Servers should be listed in order of preference. The code for the StreetTalk Directory Assistance server option is 76. The minimum length for this option is 4 octets, and the length must always be a multiple of 4.
77	User class	Specifies the class name of which the host is a member. You must have previously defined this class to the DHCP server during DHCP server configuration.
78	Directory agent	Specifies the IP address of the directory agent if clients use Service Location Protocol to transact messages.
79	Service scope	Specifies the scope of the directory agent that uses Service Location Protocol to respond to service request messages.
80	Naming authority	Specifies the naming authority for the directory agent if clients use Service Location Protocol to transact messages. The naming authority specifies the syntax for schemes that are used in URLs.

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Parent topic:

DHCP concepts

Related information
DHCP Options and BOOTP Vendor Extensions