1.\" $OpenBSD: dhcp-options.5,v 1.22 2015/09/14 20:06:59 schwarze Exp $ 2.\" 3.\" Copyright (c) 1995, 1996, 1997, 1998 The Internet Software Consortium. 4.\" All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in the 14.\" documentation and/or other materials provided with the distribution. 15.\" 3. Neither the name of The Internet Software Consortium nor the names 16.\" of its contributors may be used to endorse or promote products derived 17.\" from this software without specific prior written permission. 18.\" 19.\" THIS SOFTWARE IS PROVIDED BY THE INTERNET SOFTWARE CONSORTIUM AND 20.\" CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, 21.\" INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF 22.\" MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE 23.\" DISCLAIMED. IN NO EVENT SHALL THE INTERNET SOFTWARE CONSORTIUM OR 24.\" CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 25.\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 26.\" LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF 27.\" USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND 28.\" ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, 29.\" OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT 30.\" OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 31.\" SUCH DAMAGE. 32.\" 33.\" This software has been written for the Internet Software Consortium 34.\" by Ted Lemon <mellon@fugue.com> in cooperation with Vixie 35.\" Enterprises. To learn more about the Internet Software Consortium, 36.\" see ``http://www.isc.org/isc''. To learn more about Vixie 37.\" Enterprises, see ``http://www.vix.com''. 38.\" 39.Dd $Mdocdate: September 14 2015 $ 40.Dt DHCP-OPTIONS 5 41.Os 42.Sh NAME 43.Nm dhcp-options 44.Nd DHCP options 45.Sh DESCRIPTION 46The Dynamic Host Configuration protocol allows the client to receive 47.Ic options 48from the DHCP server describing the network configuration and various 49services that are available on the network. 50When configuring 51.Xr dhcpd 8 52or 53.Xr dhclient 8 , 54options must often be declared. 55The syntax for declaring options, and the names and formats of the options 56that can be declared, are documented here. 57.Pp 58DHCP 59.Ic option 60statements always start with the 61.Ic option 62keyword, followed by an option name, followed by option data. 63The option names and data formats are described below. 64It is not necessary to exhaustively specify all DHCP options \- 65only those options which are needed by clients must be specified. 66.Pp 67Option data comes in a variety of formats, as defined below: 68.Pp 69The 70.Ar ip-address 71data type can be entered either as an explicit IP address 72(e.g., 239.254.197.10) or as a domain name (e.g., haagen.isc.org). 73A domain name must resolve to a single IP address. 74.Pp 75The 76.Ar int32 77data type specifies a signed 32-bit integer. 78The 79.Ar uint32 80data type specifies an unsigned 32-bit integer. 81The 82.Ar int16 83and 84.Ar uint16 85data types specify signed and unsigned 16-bit integers. 86The 87.Ar int8 88and 89.Ar uint8 90data types specify signed and unsigned 8-bit integers. 91Unsigned 8-bit integers are also sometimes referred to as octets. 92.Pp 93The 94.Ar string 95data type specifies an 96.Tn NVT 97.Pq Network Virtual Terminal 98.Tn ASCII 99string, which must be enclosed in double quotes \- for example, 100to specify a domain-name option, the syntax would be 101.Pp 102.Dl option domain-name \&"isc.org\&"; 103.Pp 104The 105.Ar flag 106data type specifies a boolean value. 107Booleans can be either true or false 108(or on or off, if that makes more sense to you). 109.Pp 110The 111.Ar data-string 112data type specifies either an 113.Tn NVT ASCII 114string enclosed in double quotes, or a series of octets specified in 115hexadecimal, separated by colons. 116For example: 117.Pp 118.Dl option dhcp-client-identifier \&"CLIENT-FOO\&"; 119or 120.Dl option dhcp-client-identifier 43:4c:49:45:4e:54:2d:46:4f:4f; 121.Pp 122The documentation for the various options mentioned below is taken 123from the IETF draft document on DHCP options, RFC 2132. 124Options which are not listed by name may be defined by the name 125.Pf option- Ar nnn , 126where 127.Ar nnn 128is the decimal number of the option code. 129These options may be followed either by a string, enclosed in quotes, or by 130a series of octets, expressed as two-digit hexadecimal numbers separated 131by colons. 132For example: 133.Bd -literal -offset indent 134option option-133 "my-option-133-text"; 135option option-129 1:54:c9:2b:47; 136.Ed 137.Pp 138Because 139.Xr dhcpd 8 140does not know the format of these undefined option codes, 141no checking is done to ensure the correctness of the entered data. 142.Pp 143The defined options are: 144.Bl -tag -width Ds 145.It Ic option all-subnets-local Ar flag ; 146This option specifies whether or not the client may assume that all subnets 147of the IP network to which the client is connected use the same MTU as the 148subnet of that network to which the client is directly connected. 149A value of 1 indicates that all subnets share the same MTU. 150A value of 0 means that the client should assume that some subnets of the 151directly connected network may have smaller MTUs. 152.It Ic option arp-cache-timeout Ar uint32 ; 153This option specifies the timeout in seconds for ARP cache entries. 154.It Ic option autoproxy-script Ar string ; 155Site-specific as of RFC 3942. 156Widely used for Web Proxy Autodiscovery Protocol (WPAD). 157.It Ic option boot-size Ar uint16 ; 158This option specifies the length in 512-octet blocks of the default 159boot image for the client. 160.It Ic option bootfile-name Ar string ; 161This option is used to identify a bootstrap file. 162If supported by the client, it should have the same effect as the 163.Ic filename 164declaration. 165BOOTP clients are unlikely to support this option. 166Some DHCP clients will support it, and others actually require it. 167.It Ic option broadcast-address Ar ip-address ; 168This option specifies the broadcast address in use on the client's subnet. 169Legal values for broadcast addresses are specified in section 3.2.1.3 of 170RFC 1122. 171.It Ic option classless-static-routes Ar ip/prefix ip Oo , Ar ip/prefix ip ... Oc ; 172This option specifies a list of static routes in CDIR notation, which 173should be sent to the client. 174.It Ic option classless-ms-static-routes Ar ip/prefix ip Oo , Ar ip/prefix ip ... Oc ; 175This option does the same as 176.Ic classless-static-routes , 177but uses option code 249 instead of 121, 178since Windows XP and Windows Server 2003 ignore option 121. 179.It Ic option cookie-servers Ar ip-address Oo , Ar ip-address ... Oc ; 180The 181.Ic cookie-servers 182option specifies a list of RFC 865 cookie servers available to the client. 183Servers should be listed in order of preference. 184.It Ic option default-ip-ttl Ar uint8 ; 185This option specifies the default time-to-live that the client should 186use on outgoing datagrams. 187.It Ic option default-tcp-ttl Ar uint8 ; 188This option specifies the default TTL that the client should use when 189sending TCP segments. 190The minimum value is 1. 191.It Ic option dhcp-class-identifier Ar string ; 192This option is used by DHCP clients to optionally identify the vendor type 193and configuration of a DHCP client. 194The information is a string of n octets, interpreted by servers. 195Vendors may choose to define specific vendor class identifiers to convey 196particular configuration or other identification information about a client. 197For example, the identifier may encode the client's hardware configuration. 198Servers not equipped to interpret the class-specific information sent by a 199client must ignore it (although it may be reported). 200Servers that respond should only use option 43 201.Pq Ic vendor-encapsulated-options 202to return the vendor-specific information to the client. 203.It Ic option dhcp-client-identifier Ar data-string ; 204This option can be used to specify a DHCP client identifier in a 205host declaration, so that 206.Xr dhcpd 8 207can find the host record by matching against the client identifier. 208.It Ic option dhcp-lease-time Ar uint32 ; 209This option is used in a client request (DHCPDISCOVER or DHCPREQUEST) to 210allow the client to request a lease time for the IP address. 211In a server reply (DHCPOFFER), a DHCP server uses this option to specify the 212lease time it is willing to offer. 213.It Ic option dhcp-max-message-size Ar uint16 ; 214This option specifies the maximum length DHCP message that it is willing 215to accept. 216The length is specified as an unsigned 16-bit integer. 217A client may use the maximum DHCP message size option in DHCPDISCOVER or 218DHCPREQUEST messages, but should not use the option in DHCPDECLINE messages. 219.It Ic option dhcp-message-type Ar uint8 ; 220This option is used to convey the type of the DHCP message. 221Values: 1=DHCPDISCOVER, 2=DHCPOFFER, 3=DHCPREQUEST, 4=DHCPDECLINE, 5=DHCPACK, 2226=DHCPNAK, 7=DHCPRELEASE, 8=DHCPINFORM. 223.It Ic option dhcp-option-overload Ar uint8 Oo , Ar uint8 ... Oc ; 224This option is used to indicate that the DHCP 'sname' or 'file' fields are 225being overloaded by using them to carry DHCP options. 226A DHCP server inserts this option if the returned parameters will exceed 227the usual space allotted for options. 228If this option is present, the client interprets the specified additional 229fields after it concludes interpretation of the standard option fields. 230A value of 1 means the 'file' field is used to hold options. 231A value of 2 means the 'sname' field is used to hold options. 232A value of 3 means both fields are used to hold options. 233.It Ic option dhcp-parameter-request-list Ar uint8 Oo , Ar uint8 ... Oc ; 234This option is used by a DHCP client to request values for specified 235configuration parameters. 236The list of requested parameters is specified as n octets, where each 237octet is a valid DHCP option code as defined in this document. 238The client MAY list the options in order of preference. 239The DHCP server is not required to return the options in the requested 240order, but MUST try to insert the requested options in the order requested 241by the client. 242.It Ic option dhcp-rebinding-time Ar uint32 ; 243This option specifies the time interval from address assignment until the 244client transitions to the REBINDING state. 245The value is in seconds. 246.It Ic option dhcp-renewal-time Ar uint32 ; 247This option specifies the time interval from address assignment until the 248client transitions to the RENEWING state. 249The value is in seconds. 250.It Ic option dhcp-requested-address Ar ip-address ; 251This option is used in a client request (DHCPDISCOVER) to allow the client 252to request that a particular IP address be assigned. 253.It Ic option dhcp-server-identifier Ar ip-address ; 254This option is used in DHCPOFFER and DHCPREQUEST messages, and may 255optionally be included in the DHCPACK and DHCPNAK messages. 256DHCP servers include this option in the DHCPOFFER in order to allow the 257client to distinguish between lease offers. 258DHCP clients use the contents of the 'server identifier' field as the 259destination address for any DHCP messages unicast to the DHCP server. 260DHCP clients also indicate which of several lease offers is being accepted 261by including this option in a DHCPREQUEST message. 262The identifier is the IP address of the selected server. 263.It Ic option domain-name Ar string ; 264This option specifies the domain name that the client should use when 265resolving hostnames via the Domain Name System. 266.It Ic option domain-name-servers Ar ip-address Oo , Ar ip-address ... Oc ; 267The 268.Ic domain-name-servers 269option specifies a list of Domain Name System name servers 270available to the client. 271Servers should be listed in order of preference. 272.It Ic option extensions-path Ar string ; 273A string to specify a file, retrievable via TFTP, which contains information 274which can be interpreted in the same way as the 64-octet vendor-extension 275field within the BOOTP response, with exceptions; see RFC 2132, Section 3.20 276for details. 277.It Ic option finger-server Ar ip-address Oo , Ar ip-address ... Oc ; 278The 279.Ic finger-server 280option specifies a list of 281.Xr finger 1 282servers available to the client. 283Servers should be listed in order of preference. 284.It Ic option font-servers Ar ip-address Oo , Ar ip-address ... Oc ; 285This option specifies a list of X Window System Font servers available 286to the client. 287Servers should be listed in order of preference. 288.It Ic option host-name Ar string ; 289This option specifies the name of the client. 290The name may or may not be qualified with the local domain name 291(it is preferable to use the 292.Ic domain-name 293option to specify the domain name). 294See RFC 1035 for character set restrictions. 295.It Ic option ieee802-3-encapsulation Ar flag ; 296This option specifies whether or not the client should use Ethernet 297Version 2 (RFC 894) or IEEE 802.3 (RFC 1042) encapsulation if the 298interface is an Ethernet. 299A value of 0 indicates that the client should use RFC 894 encapsulation. 300A value of 1 means that the client should use RFC 1042 encapsulation. 301.It Ic option ien116-name-servers Ar ip-address Oo , Ar ip-address ... Oc ; 302The 303.Ic ien116-name-servers 304option specifies a list of IEN 116 name servers available to the client. 305Servers should be listed in order of preference. 306.It Ic option impress-servers Ar ip-address Oo , Ar ip-address ... Oc ; 307The 308.Ic impress-servers 309option specifies a list of Imagen Impress servers available to the client. 310Servers should be listed in order of preference. 311.It Ic option interface-mtu Ar uint16 ; 312This option specifies the MTU to use on this interface. 313The minimum legal value for the MTU is 68. 314.It Ic option ip-forwarding Ar flag ; 315This option specifies whether the client should configure its IP layer 316for packet forwarding. 317A value of 0 means disable IP forwarding, and a value of 1 means enable 318IP forwarding. 319.It Ic option irc-server Ar ip-address Oo , Ar ip-address ... Oc ; 320The 321.Ic irc-server 322option specifies a list of IRC servers available to the client. 323Servers should be listed in order of preference. 324.It Ic option log-servers Ar ip-address Oo , Ar ip-address ... Oc ; 325The 326.Ic log-servers 327option specifies a list of MIT-LCS UDP log servers available to the client. 328Servers should be listed in order of preference. 329.It Ic option lpr-servers Ar ip-address Oo , Ar ip-address ... Oc ; 330The 331.Ic lpr-servers 332option specifies a list of RFC 1179 line printer servers available to the 333client. 334Servers should be listed in order of preference. 335.It Ic option mask-supplier Ar flag ; 336This option specifies whether or not the client should respond to subnet mask 337requests using ICMP. 338A value of 0 indicates that the client should not respond. 339A value of 1 means that the client should respond. 340.It Ic option max-dgram-reassembly Ar uint16 ; 341This option specifies the maximum size datagram that the client should be 342prepared to reassemble. 343The minimum legal value is 576. 344.It Ic option merit-dump Ar string ; 345This option specifies the pathname of a file to which the client's 346core image should be dumped in the event the client crashes. 347The path is formatted as a character string consisting of characters from 348the 349.Tn NVT ASCII 350character set. 351.It Ic option mobile-ip-home-agent Ar ip-address Oo , Ar ip-address ... Oc ; 352This option specifies a list of IP addresses indicating Mobile IP 353home agents available to the client. 354Agents should be listed in order of preference, although normally there 355will be only one such agent. 356.It Ic option nds-context Ar string ; 357This option specifies the initial NDS context the client should use. 358NDS contexts are 16-bit Unicode strings. 359For transmission in the NDS Context Option, an NDS context is 360transformed into octets using UTF-8. 361The string should NOT be zero terminated. 362A single DHCP option can only contain 255 octets. 363Since an NDS context name can be longer than that, this option can 364appear more than once in the DHCP packet. 365The contents of all NDS Context options in the packet should be 366concatenated as suggested in the DHCP specification to get the 367complete NDS context. 368A single encoded character could be split between two NDS Context Options. 369See RFC 2241 for details. 370.It Ic option nds-servers Ar ip-address Oo , Ar ip-address ... Oc ; 371This option specifies one or more NDS servers for the client to contact 372for access to the NDS database. 373Servers should be listed in order of preference. 374See RFC 2241 for details. 375.It Ic option nds-tree-name Ar string ; 376This option specifies the name of the NDS tree the client will be contacting. 377NDS tree names are 16-bit Unicode strings. 378For transmission in the NDS Tree Name Option, an NDS tree name is 379transformed into octets using UTF-8. 380The string should not be zero terminated. 381See RFC 2241 for details. 382.It Ic option netbios-dd-server Ar ip-address Oo , Ar ip-address ... Oc ; 383The NetBIOS datagram distribution server (NBDD) option specifies a 384list of RFC 1001/1002 NBDD servers listed in order of preference. 385.It Ic option netbios-name-servers Ar ip-address Oo , Ar ip-address ... Oc ; 386The NetBIOS name server (NBNS) option specifies a list of RFC 1001/1002 387NBNS name servers listed in order of preference. 388NetBIOS Name Service is currently more commonly referred to as WINS. 389WINS servers can be specified using the 390.Ic netbios-name-servers 391option. 392.It Ic option netbios-node-type Ar uint8 ; 393The NetBIOS node type option allows NetBIOS over TCP/IP clients which 394are configurable to be configured as described in RFC 1001/1002. 395The value is specified as a single octet which identifies the client type. 396.Pp 397Possible node types are: 398.Bl -tag -width Ds 399.It 1 400B-node: Broadcast - no WINS 401.It 2 402P-node: Peer - WINS only 403.It 4 404M-node: Mixed - broadcast, then WINS 405.It 8 406H-node: Hybrid - WINS, then broadcast 407.El 408.It Ic option netbios-scope Ar string ; 409The NetBIOS scope option specifies the NetBIOS over TCP/IP scope 410parameter for the client as specified in RFC 1001/1002. 411See RFC 1001, RFC 1002, and RFC 1035 for character-set restrictions. 412.It Ic option nis-domain Ar string ; 413This option specifies the name of the client's NIS (Sun Network Information 414Services) domain. 415The domain is formatted as a character string consisting of characters 416from the 417.Tn NVT ASCII 418character set. 419.It Ic option nis-servers Ar ip-address Oo , Ar ip-address ... Oc ; 420This option specifies a list of IP addresses indicating NIS servers 421available to the client. 422Servers should be listed in order of preference. 423.It Ic option nisplus-domain Ar string ; 424This option specifies the name of the client's NIS+ domain. 425The domain is formatted as a character string consisting of characters 426from the 427.Tn NVT ASCII 428character set. 429.It Ic option nisplus-servers Ar ip-address Oo , Ar ip-address ... Oc ; 430This option specifies a list of IP addresses indicating NIS+ servers 431available to the client. 432Servers should be listed in order of preference. 433.It Ic option nntp-server Ar ip-address Oo , Ar ip-address ... Oc ; 434The 435.Ic nntp-server 436option specifies a list of NNTP servers available to the client. 437Servers should be listed in order of preference. 438.It Ic option non-local-source-routing Ar flag ; 439This option specifies whether the client should configure its IP 440layer to allow forwarding of datagrams with non-local source routes. 441A value of 0 means disallow forwarding of such datagrams, and a value of 1 442means allow forwarding. 443.It Ic option ntp-servers Ar ip-address Oo , Ar ip-address ... Oc ; 444This option specifies a list of IP addresses indicating NTP (RFC 5905) 445servers available to the client. 446Servers should be listed in order of preference. 447.It Ic option path-mtu-aging-timeout Ar uint32 ; 448This option specifies the timeout (in seconds) to use when aging Path 449MTU values discovered by the mechanism defined in RFC 1191. 450.It Ic option path-mtu-plateau-table Ar uint16 Oo , Ar uint16 ... Oc ; 451This option specifies a table of MTU sizes to use when performing 452Path MTU Discovery as defined in RFC 1191. 453The table is formatted as a list of 16-bit unsigned integers, 454ordered from smallest to largest. 455The minimum MTU value cannot be smaller than 68. 456.It Ic option perform-mask-discovery Ar flag ; 457This option specifies whether or not the client should perform subnet mask 458discovery using ICMP. 459A value of 0 indicates that the client should not perform mask discovery. 460A value of 1 means that the client should perform mask discovery. 461.It Ic option policy-filter Ar ip-address ip-address Oo , Ar ip-address ip-address ... Oc ; 462This option specifies policy filters for non-local source routing. 463The filters consist of a list of IP addresses and masks which specify 464destination/mask pairs with which to filter incoming source routes. 465.Pp 466Any source-routed datagram whose next-hop address does not match one 467of the filters should be discarded by the client. 468.Pp 469See RFC 1122 for further information. 470.It Ic option pop-server Ar ip-address Oo , Ar ip-address ... Oc ; 471The 472.Ic pop-server 473option specifies a list of POP3 servers available to the client. 474Servers should be listed in order of preference. 475.It Ic option relay-agent-information Ar string ; 476This is a "container" option for specific agent-supplied sub-options. 477See RFC 3046 for details. 478.It Ic option resource-location-servers Ar ip-address Oo , Ar ip-address ... Oc ; 479This option specifies a list of RFC 887 Resource Location servers available 480to the client. 481Servers should be listed in order of preference. 482.It Ic option root-path Ar string ; 483This option specifies the pathname that contains the client's root disk. 484The path is formatted as a character string consisting of characters from 485the 486.Tn NVT ASCII 487character set. 488.It Ic option router-discovery Ar flag ; 489This option specifies whether or not the client should solicit routers using 490the Router Discovery mechanism defined in RFC 1256. 491A value of 0 indicates that the client should not perform router discovery. 492A value of 1 means that the client should perform router discovery. 493.It Ic option router-solicitation-address Ar ip-address ; 494This option specifies the address to which the client should transmit 495router solicitation requests. 496.It Ic option routers Ar ip-address Oo , Ar ip-address ... Oc ; 497The 498.Ic routers 499option specifies a list of IP addresses for routers on the client's subnet. 500Routers should be listed in order of preference. 501.It Ic option smtp-server Ar ip-address Oo , Ar ip-address ... Oc ; 502The 503.Ic smtp-server 504option specifies a list of SMTP servers available to the client. 505Servers should be listed in order of preference. 506.It Ic option static-routes Ar ip-address ip-address Oo , Ar ip-address ip-address ... Oc ; 507This option specifies a list of static routes that the client should 508install in its routing cache. 509If multiple routes to the same destination are specified, they are listed 510in descending order of priority. 511.Pp 512The routes consist of a list of IP address pairs. 513The first address is the destination address, 514and the second address is the router for the destination. 515.Pp 516The default route (0.0.0.0) is an illegal destination for a static route. 517To specify the default route, use the 518.Ic routers 519option. 520.It Ic option streettalk-directory-assistance-server Ar ip-address Oo , Ar ip-address ... Oc ; 521The StreetTalk Directory Assistance (STDA) server option specifies a 522list of STDA servers available to the client. 523Servers should be listed in order of preference. 524.It Ic option streettalk-server Ar ip-address Oo , Ar ip-address ... Oc ; 525The 526.Ic streettalk-server 527option specifies a list of StreetTalk servers available to the client. 528Servers should be listed in order of preference. 529.It Ic option subnet-mask Ar ip-address ; 530The 531.Ic subnet-mask 532option specifies the client's subnet mask as per RFC 950. 533If no subnet-mask option is provided anywhere in scope, as a last resort 534.Xr dhcpd 8 535will use the subnet mask from the subnet declaration for the network on 536which an address is being assigned. 537However, 538.Em any 539subnet-mask option declaration that is in scope for the address being 540assigned will override the subnet mask specified in the subnet declaration. 541.It Ic option swap-server Ar ip-address ; 542This specifies the IP address of the client's swap server. 543.It Ic option tcp-keepalive-garbage Ar flag ; 544This option specifies whether or not the client should send TCP keepalive 545messages with an octet of garbage for compatibility with older implementations. 546A value of 0 indicates that a garbage octet should not be sent. 547A value of 1 indicates that a garbage octet should be sent. 548.It Ic option tcp-keepalive-interval Ar uint32 ; 549This option specifies the interval (in seconds) that the client TCP 550should wait before sending a keepalive message on a TCP connection. 551The time is specified as a 32-bit unsigned integer. 552A value of zero indicates that the client should not generate keepalive 553messages on connections unless specifically requested by an application. 554.It Ic option tftp-config-file Ar string ; 555Option 144. 556Per RFC 2132 options 128 \- 254 are site-specific. 557RFC 3942 reclassifies options 128 to 223 as publicly defined options and 558puts them in "Unavailable" state by IANA. 559See RFC 3679 for "Unused DHCP Option Codes to be Reassigned to Future 560DHCP Options". 561See RFC 2939 for procedures for definitions of new DHCP options. 562.It Ic option tftp-server-name Ar string ; 563This option is used to identify a TFTP server and, if supported by the 564client, should have the same effect as the 565.Ic server-name 566declaration. 567BOOTP clients are unlikely to support this option. 568Some DHCP clients will support it, and others actually require it. 569.It Ic option time-offset Ar int32 ; 570The 571.Ic time-offset 572option specifies the offset of the client's subnet in seconds from 573Coordinated Universal Time (UTC). 574.It Ic option time-servers Ar ip-address Oo , Ar ip-address ... Oc ; 575The 576.Ic time-server 577option specifies a list of RFC 868 time servers available to the client. 578Servers should be listed in order of preference. 579.It Ic option trailer-encapsulation Ar flag ; 580This option specifies whether or not the client should negotiate the 581use of trailers (RFC 893) when using the ARP protocol. 582A value of 0 indicates that the client should not attempt to use trailers. 583A value of 1 means that the client should attempt to use trailers. 584.It Ic option user-class Ar string ; 585This option is used by a DHCP client to optionally identify the type or 586category of user or applications it represents. 587A DHCP server uses the User Class option to choose the address pool it 588allocates an address from and/or to select any other configuration option. 589This option may carry multiple User Classes. 590Servers may interpret the meanings of multiple class specifications in an 591implementation dependent or configuration dependent manner, and so the use 592of multiple classes by a DHCP client should be based on the specific server 593implementation and configuration which will be used to process that User 594class option. 595See RFC 3004 for details. 596.It Ic option vendor-encapsulated-options Ar data-string ; 597This option is used by clients and servers to exchange vendor-specific 598information. 599The information is an opaque object of n octets, presumably interpreted by 600vendor-specific code on the clients and servers. 601See RFC 2132, Section 8.4 for details. 602.It Ic option voip-configuration-server Ar ip-address Oo , Ar ip-address ... Oc ; 603The 604.Ic voip-configuration-server 605option specifies a list of (normally TFTP) servers that VoIP clients 606may download their configuration information and software images 607from. 608Servers should be listed in order of preference. 609.It Ic option www-server Ar ip-address Oo , Ar ip-address ... Oc ; 610The 611.Ic www-server 612option specifies a list of WWW servers available to the client. 613.It Ic option x-display-manager Ar ip-address Oo , Ar ip-address ... Oc ; 614This option specifies a list of systems that are running the X Window 615System Display Manager and are available to the client. 616Addresses should be listed in order of preference. 617.El 618.Sh SEE ALSO 619.Xr dhclient.conf 5 , 620.Xr dhcpd.conf 5 , 621.Xr dhcpd.leases 5 , 622.Xr dhclient 8 , 623.Xr dhcpd 8 624.Sh STANDARDS 625.Rs 626.%A R. Droms 627.%D October 1993 628.%R RFC 1534 629.%T Interoperation Between DHCP and BOOTP 630.Re 631.Pp 632.Rs 633.%A R. Droms 634.%D March 1997 635.%R RFC 2131 636.%T Dynamic Host Configuration Protocol 637.Re 638.Pp 639.Rs 640.%A S. Alexander 641.%A R. Droms 642.%D March 1997 643.%R RFC 2132 644.%T DHCP Options and BOOTP Vendor Extensions 645.Re 646.Pp 647.Rs 648.%A T. Lemon 649.%A S. Cheshire 650.%D November 2002 651.%R RFC 3396 652.%T Encoding Long Options in the Dynamic Host Configuration Protocol (DHCPv4) 653.Re 654.Pp 655.Rs 656.%A T. Lemon 657.%A S. Cheshire 658.%A B. Volz 659.%D December 2002 660.%R RFC 3442 661.%T The Classless Static Route Option for Dynamic Host Configuration Protocol (DHCP) version 4 662.Re 663.Sh AUTHORS 664.An -nosplit 665.Xr dhcpd 8 666was written by 667.An Ted Lemon Aq Mt mellon@vix.com 668under a contract with Vixie Labs. 669.Pp 670The current implementation was reworked by 671.An Henning Brauer Aq Mt henning@openbsd.org . 672