1.\" $OpenBSD: dhcp-options.5,v 1.30 2019/04/02 03:21:21 krw 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: April 2 2019 $ 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 cidr 77data type specifies a network in CIDR notion. 78e.g. 1.2.3/24. 79.Pp 80The 81.Ar rfc1035 82data type specifies a list of domain names compressed 83as described in Section 4.1.4 of RFC 1035. 84The compressed list takes the form of a series of 85octets specified in hexadecimal, separated by colons. 86.Pp 87The 88.Ar int32 89data type specifies a signed 32-bit integer. 90The 91.Ar uint32 92data type specifies an unsigned 32-bit integer. 93The 94.Ar uint16 95data type specifies unsigned 16-bit integers. 96The 97.Ar uint8 98data type specifies unsigned 8-bit integers, 99sometimes referred to as octets. 100.Pp 101The 102.Ar string 103data type specifies an 104.Tn NVT 105.Pq Network Virtual Terminal 106.Tn ASCII 107string, which must be enclosed in double quotes \- for example, 108to specify a domain-name option, the syntax would be 109.Pp 110.Dl option domain-name \&"isc.org\&"; 111.Pp 112The 113.Ar flag 114data type specifies a boolean value. 115Booleans can be either true or false 116(or on or off, if that makes more sense to you). 117.Pp 118The 119.Ar data-string 120data type specifies either an 121.Tn NVT ASCII 122string enclosed in double quotes, or a series of octets specified in 123hexadecimal, separated by colons. 124For example: 125.Pp 126.Dl option dhcp-client-identifier \&"CLIENT-FOO\&"; 127or 128.Dl option dhcp-client-identifier 43:4c:49:45:4e:54:2d:46:4f:4f; 129.Pp 130The documentation for the various options mentioned below is taken 131from the IETF draft document on DHCP options, RFC 2132. 132Options which are not listed by name may be defined by the name 133.Pf option- Ar nnn , 134where 135.Ar nnn 136is the decimal number of the option code. 137These options may be followed either by a string, enclosed in quotes, or by 138a series of octets, expressed as two-digit hexadecimal numbers separated 139by colons. 140For example: 141.Bd -literal -offset indent 142option option-133 "my-option-133-text"; 143option option-129 1:54:c9:2b:47; 144.Ed 145.Pp 146Because 147.Xr dhcpd 8 148does not know the format of these undefined option codes, 149no checking is done to ensure the correctness of the entered data. 150.Pp 151The defined options are: 152.Bl -tag -width Ds 153.It Ic option all-subnets-local Ar flag ; 154This option specifies whether or not the client may assume that all subnets 155of the IP network to which the client is connected use the same MTU as the 156subnet of that network to which the client is directly connected. 157A value of 1 indicates that all subnets share the same MTU. 158A value of 0 means that the client should assume that some subnets of the 159directly connected network may have smaller MTUs. 160.It Ic option arp-cache-timeout Ar uint32 ; 161This option specifies the timeout in seconds for ARP cache entries. 162.It Ic option autoproxy-script Ar string ; 163Site-specific as of RFC 3942. 164Widely used for Web Proxy Autodiscovery Protocol (WPAD). 165.It Ic option boot-size Ar uint16 ; 166This option specifies the length in 512-octet blocks of the default 167boot image for the client. 168.It Ic option bootfile-name Ar string ; 169This option is used to identify a bootstrap file. 170If supported by the client, it should have the same effect as the 171.Ic filename 172declaration. 173BOOTP clients are unlikely to support this option. 174Some DHCP clients will support it, and others actually require it. 175.It Ic option broadcast-address Ar ip-address ; 176This option specifies the broadcast address in use on the client's subnet. 177Legal values for broadcast addresses are specified in section 3.2.1.3 of 178RFC 1122. 179.It Ic option classless-static-routes Ar cidr ip-address Oo , Ar cidr ip-address ... Oc ; 180This option specifies a list of destination networks and the 181associated gateways. 182This option is defined in RFC 3442. 183The RFC says that clients supporting this option must ignore the 184.Ic Routers 185option when both are present. 186Thus default routes, if any, 187must be included in the list. 188The 189.Ar cidr 190of a default route is 0/0. 191.It Ic option classless-ms-static-routes Ar cidr ip-address Oo , Ar cidr ip-address ... Oc ; 192This option does the same as 193.Ic classless-static-routes , 194but uses option code 249 instead of 121, 195since Windows XP and Windows Server 2003 ignore option 121. 196.It Ic option cookie-servers Ar ip-address Oo , Ar ip-address ... Oc ; 197The 198.Ic cookie-servers 199option specifies a list of RFC 865 cookie servers available to the client. 200Servers should be listed in order of preference. 201.It Ic option default-ip-ttl Ar uint8 ; 202This option specifies the default time-to-live that the client should 203use on outgoing datagrams. 204.It Ic option default-tcp-ttl Ar uint8 ; 205This option specifies the default TTL that the client should use when 206sending TCP segments. 207The minimum value is 1. 208.It Ic option dhcp-class-identifier Ar string ; 209This option is used by DHCP clients to optionally identify the vendor type 210and configuration of a DHCP client. 211The information is a string of n octets, interpreted by servers. 212Vendors may choose to define specific vendor class identifiers to convey 213particular configuration or other identification information about a client. 214For example, the identifier may encode the client's hardware configuration. 215Servers not equipped to interpret the class-specific information sent by a 216client must ignore it (although it may be reported). 217Servers that respond should only use option 43 218.Pq Ic vendor-encapsulated-options 219to return the vendor-specific information to the client. 220.It Ic option dhcp-client-identifier Ar data-string ; 221This option can be used to specify a DHCP client identifier in a 222host declaration, so that 223.Xr dhcpd 8 224can find the host record by matching against the client identifier. 225.It Ic option dhcp-lease-time Ar uint32 ; 226This option is used in a client request (DHCPDISCOVER or DHCPREQUEST) to 227allow the client to request a lease time for the IP address. 228In a server reply (DHCPOFFER), a DHCP server uses this option to specify the 229lease time it is willing to offer. 230.It Ic option dhcp-max-message-size Ar uint16 ; 231This option specifies the maximum length 232.Ic option dhcp-message 233that the DHCP client is willing to accept. 234The length is specified as an unsigned 16-bit integer. 235A client may use the maximum DHCP message size option in DHCPDISCOVER or 236DHCPREQUEST messages, but should not use the option in DHCPDECLINE messages. 237.It Ic option dhcp-message Ar string ; 238This option is used to send an error message to a DHCP client in 239the event of a failure. 240The maximum acceptable length of the message can be set with 241.Ic option dhcp-max-message-size . 242.It Ic option dhcp-message-type Ar uint8 ; 243This option is used to convey the type of the DHCP message. 244Values: 1=DHCPDISCOVER, 2=DHCPOFFER, 3=DHCPREQUEST, 4=DHCPDECLINE, 5=DHCPACK, 2456=DHCPNAK, 7=DHCPRELEASE, 8=DHCPINFORM. 246.It Ic option dhcp-option-overload Ar uint8 ; 247This option is used to indicate that the DHCP 'sname' or 'file' fields are 248being overloaded by using them to carry DHCP options. 249A DHCP server inserts this option if the returned parameters will exceed 250the usual space allotted for options. 251If this option is present, the client interprets the specified additional 252fields after it concludes interpretation of the standard option fields. 253A value of 1 means the 'file' field is used to hold options. 254A value of 2 means the 'sname' field is used to hold options. 255A value of 3 means both fields are used to hold options. 256.It Ic option dhcp-parameter-request-list Ar uint8 Oo , Ar uint8 ... Oc ; 257This option is used by a DHCP client to request values for specified 258configuration parameters. 259The list of requested parameters is specified as n octets, where each 260octet is a valid DHCP option code as defined in this document. 261The client MAY list the options in order of preference. 262The DHCP server is not required to return the options in the requested 263order, but MUST try to insert the requested options in the order requested 264by the client. 265.It Ic option dhcp-rebinding-time Ar uint32 ; 266This option specifies the time interval from address assignment until the 267client transitions to the REBINDING state. 268The value is in seconds. 269.It Ic option dhcp-renewal-time Ar uint32 ; 270This option specifies the time interval from address assignment until the 271client transitions to the RENEWING state. 272The value is in seconds. 273.It Ic option dhcp-requested-address Ar ip-address ; 274This option is used in a client request (DHCPDISCOVER) to allow the client 275to request that a particular IP address be assigned. 276.It Ic option dhcp-server-identifier Ar ip-address ; 277This option is used in DHCPOFFER and DHCPREQUEST messages, and may 278optionally be included in the DHCPACK and DHCPNAK messages. 279DHCP servers include this option in the DHCPOFFER in order to allow the 280client to distinguish between lease offers. 281DHCP clients use the contents of the 'server identifier' field as the 282destination address for any DHCP messages unicast to the DHCP server. 283DHCP clients also indicate which of several lease offers is being accepted 284by including this option in a DHCPREQUEST message. 285The identifier is the IP address of the selected server. 286.It Ic option domain-name Ar string ; 287This option specifies the domain name that the client should use when 288resolving hostnames via the Domain Name System. 289.It Ic option domain-name-servers Ar ip-address Oo , Ar ip-address ... Oc ; 290The 291.Ic domain-name-servers 292option specifies a list of Domain Name System name servers 293available to the client. 294Servers should be listed in order of preference. 295.It Ic option domain-search Ar rfc1035 ; | Ar string Oo , Ar string ... Oc ; 296The 297.Ic domain-search 298option specifies a list of the domain names that should be 299used during DNS name resolution. 300.Pp 301When 302.Xr dhclient 8 303constructs 304.Xr resolv.conf 5 305it will use this list of domains in preference to any information 306provided by the 307.Ic domain-name 308option. 309.Pp 310Note that 311.Xr dhcpd 8 312calls this option 313.Ic option-119 314instead of 315.Ic domain-search 316and only supports the 317.Ar rfc1035 318variant. 319.It Ic option extensions-path Ar string ; 320A string to specify a file, retrievable via TFTP, which contains information 321which can be interpreted in the same way as the 64-octet vendor-extension 322field within the BOOTP response, with exceptions; see RFC 2132, Section 3.20 323for details. 324.It Ic option finger-server Ar ip-address Oo , Ar ip-address ... Oc ; 325The 326.Ic finger-server 327option specifies a list of 328.Xr finger 1 329servers available to the client. 330Servers should be listed in order of preference. 331.It Ic option font-servers Ar ip-address Oo , Ar ip-address ... Oc ; 332This option specifies a list of X Window System Font servers available 333to the client. 334Servers should be listed in order of preference. 335.It Ic option host-name Ar string ; 336This option specifies the name of the client. 337The name may or may not be qualified with the local domain name 338(it is preferable to use the 339.Ic domain-name 340option to specify the domain name). 341See RFC 1035 for character set restrictions. 342.It Ic option ieee802-3-encapsulation Ar flag ; 343This option specifies whether or not the client should use Ethernet 344Version 2 (RFC 894) or IEEE 802.3 (RFC 1042) encapsulation if the 345interface is an Ethernet. 346A value of 0 indicates that the client should use RFC 894 encapsulation. 347A value of 1 means that the client should use RFC 1042 encapsulation. 348.It Ic option ien116-name-servers Ar ip-address Oo , Ar ip-address ... Oc ; 349The 350.Ic ien116-name-servers 351option specifies a list of IEN 116 name servers available to the client. 352Servers should be listed in order of preference. 353.It Ic option impress-servers Ar ip-address Oo , Ar ip-address ... Oc ; 354The 355.Ic impress-servers 356option specifies a list of Imagen Impress servers available to the client. 357Servers should be listed in order of preference. 358.It Ic option interface-mtu Ar uint16 ; 359This option specifies the MTU to use on this interface. 360The minimum legal value for the MTU is 68. 361.It Ic option ip-forwarding Ar flag ; 362This option specifies whether the client should configure its IP layer 363for packet forwarding. 364A value of 0 means disable IP forwarding, and a value of 1 means enable 365IP forwarding. 366.It Ic option irc-server Ar ip-address Oo , Ar ip-address ... Oc ; 367The 368.Ic irc-server 369option specifies a list of IRC servers available to the client. 370Servers should be listed in order of preference. 371.It Ic option log-servers Ar ip-address Oo , Ar ip-address ... Oc ; 372The 373.Ic log-servers 374option specifies a list of MIT-LCS UDP log servers available to the client. 375Servers should be listed in order of preference. 376.It Ic option lpr-servers Ar ip-address Oo , Ar ip-address ... Oc ; 377The 378.Ic lpr-servers 379option specifies a list of RFC 1179 line printer servers available to the 380client. 381Servers should be listed in order of preference. 382.It Ic option mask-supplier Ar flag ; 383This option specifies whether or not the client should respond to subnet mask 384requests using ICMP. 385A value of 0 indicates that the client should not respond. 386A value of 1 means that the client should respond. 387.It Ic option max-dgram-reassembly Ar uint16 ; 388This option specifies the maximum size datagram that the client should be 389prepared to reassemble. 390The minimum legal value is 576. 391.It Ic option merit-dump Ar string ; 392This option specifies the pathname of a file to which the client's 393core image should be dumped in the event the client crashes. 394The path is formatted as a character string consisting of characters from 395the 396.Tn NVT ASCII 397character set. 398.It Ic option mobile-ip-home-agent Ar ip-address Oo , Ar ip-address ... Oc ; 399This option specifies a list of IP addresses indicating Mobile IP 400home agents available to the client. 401Agents should be listed in order of preference, although normally there 402will be only one such agent. 403.It Ic option nds-context Ar data-string ; 404This option specifies the initial NDS context the client should use. 405NDS contexts are 16-bit Unicode strings. 406For transmission in the NDS Context Option, an NDS context is 407transformed into octets using UTF-8. 408The string should NOT be zero terminated. 409A single DHCP option can only contain 255 octets. 410Since an NDS context name can be longer than that, this option can 411appear more than once in the DHCP packet. 412The contents of all NDS Context options in the packet should be 413concatenated as suggested in the DHCP specification to get the 414complete NDS context. 415A single encoded character could be split between two NDS Context Options. 416See RFC 2241 for details. 417.It Ic option nds-servers Ar ip-address Oo , Ar ip-address ... Oc ; 418This option specifies one or more NDS servers for the client to contact 419for access to the NDS database. 420Servers should be listed in order of preference. 421See RFC 2241 for details. 422.It Ic option nds-tree-name Ar data-string ; 423This option specifies the name of the NDS tree the client will be contacting. 424NDS tree names are 16-bit Unicode strings. 425For transmission in the NDS Tree Name Option, an NDS tree name is 426transformed into octets using UTF-8. 427The string should not be zero terminated. 428See RFC 2241 for details. 429.It Ic option netbios-dd-server Ar ip-address Oo , Ar ip-address ... Oc ; 430The NetBIOS datagram distribution server (NBDD) option specifies a 431list of RFC 1001/1002 NBDD servers listed in order of preference. 432.It Ic option netbios-name-servers Ar ip-address Oo , Ar ip-address ... Oc ; 433The NetBIOS name server (NBNS) option specifies a list of RFC 1001/1002 434NBNS name servers listed in order of preference. 435NetBIOS Name Service is currently more commonly referred to as WINS. 436WINS servers can be specified using the 437.Ic netbios-name-servers 438option. 439.It Ic option netbios-node-type Ar uint8 ; 440The NetBIOS node type option allows NetBIOS over TCP/IP clients which 441are configurable to be configured as described in RFC 1001/1002. 442The value is specified as a single octet which identifies the client type. 443.Pp 444Possible node types are: 445.Bl -tag -width Ds 446.It 1 447B-node: Broadcast - no WINS 448.It 2 449P-node: Peer - WINS only 450.It 4 451M-node: Mixed - broadcast, then WINS 452.It 8 453H-node: Hybrid - WINS, then broadcast 454.El 455.It Ic option netbios-scope Ar string ; 456The NetBIOS scope option specifies the NetBIOS over TCP/IP scope 457parameter for the client as specified in RFC 1001/1002. 458See RFC 1001, RFC 1002, and RFC 1035 for character-set restrictions. 459.It Ic option nis-domain Ar string ; 460This option specifies the name of the client's NIS (Sun Network Information 461Services) domain. 462The domain is formatted as a character string consisting of characters 463from the 464.Tn NVT ASCII 465character set. 466.It Ic option nis-servers Ar ip-address Oo , Ar ip-address ... Oc ; 467This option specifies a list of IP addresses indicating NIS servers 468available to the client. 469Servers should be listed in order of preference. 470.It Ic option nisplus-domain Ar string ; 471This option specifies the name of the client's NIS+ domain. 472The domain is formatted as a character string consisting of characters 473from the 474.Tn NVT ASCII 475character set. 476.It Ic option nisplus-servers Ar ip-address Oo , Ar ip-address ... Oc ; 477This option specifies a list of IP addresses indicating NIS+ servers 478available to the client. 479Servers should be listed in order of preference. 480.It Ic option nntp-server Ar ip-address Oo , Ar ip-address ... Oc ; 481The 482.Ic nntp-server 483option specifies a list of NNTP servers available to the client. 484Servers should be listed in order of preference. 485.It Ic option non-local-source-routing Ar flag ; 486This option specifies whether the client should configure its IP 487layer to allow forwarding of datagrams with non-local source routes. 488A value of 0 means disallow forwarding of such datagrams, and a value of 1 489means allow forwarding. 490.It Ic option ntp-servers Ar ip-address Oo , Ar ip-address ... Oc ; 491This option specifies a list of IP addresses indicating NTP (RFC 5905) 492servers available to the client. 493Servers should be listed in order of preference. 494.It Ic option path-mtu-aging-timeout Ar uint32 ; 495This option specifies the timeout (in seconds) to use when aging Path 496MTU values discovered by the mechanism defined in RFC 1191. 497.It Ic option path-mtu-plateau-table Ar uint16 Oo , Ar uint16 ... Oc ; 498This option specifies a table of MTU sizes to use when performing 499Path MTU Discovery as defined in RFC 1191. 500The table is formatted as a list of 16-bit unsigned integers, 501ordered from smallest to largest. 502The minimum MTU value cannot be smaller than 68. 503.It Ic option perform-mask-discovery Ar flag ; 504This option specifies whether or not the client should perform subnet mask 505discovery using ICMP. 506A value of 0 indicates that the client should not perform mask discovery. 507A value of 1 means that the client should perform mask discovery. 508.It Ic option policy-filter Ar ip-address ip-address Oo , Ar ip-address ip-address ... Oc ; 509This option specifies policy filters for non-local source routing. 510The filters consist of a list of IP addresses and masks which specify 511destination/mask pairs with which to filter incoming source routes. 512.Pp 513Any source-routed datagram whose next-hop address does not match one 514of the filters should be discarded by the client. 515.Pp 516See RFC 1122 for further information. 517.It Ic option pop-server Ar ip-address Oo , Ar ip-address ... Oc ; 518The 519.Ic pop-server 520option specifies a list of POP3 servers available to the client. 521Servers should be listed in order of preference. 522.It Ic option relay-agent-information Ar data-string ; 523This is a "container" option for specific agent-supplied sub-options. 524See RFC 3046 for details. 525.It Ic option resource-location-servers Ar ip-address Oo , Ar ip-address ... Oc ; 526This option specifies a list of RFC 887 Resource Location servers available 527to the client. 528Servers should be listed in order of preference. 529.It Ic option root-path Ar string ; 530This option specifies the pathname that contains the client's root disk. 531The path is formatted as a character string consisting of characters from 532the 533.Tn NVT ASCII 534character set. 535.It Ic option router-discovery Ar flag ; 536This option specifies whether or not the client should solicit routers using 537the Router Discovery mechanism defined in RFC 1256. 538A value of 0 indicates that the client should not perform router discovery. 539A value of 1 means that the client should perform router discovery. 540.It Ic option router-solicitation-address Ar ip-address ; 541This option specifies the address to which the client should transmit 542router solicitation requests. 543.It Ic option routers Ar ip-address Oo , Ar ip-address ... Oc ; 544The 545.Ic routers 546option specifies a list of IP addresses for routers on the client's subnet. 547Routers should be listed in order of preference. 548.It Ic option smtp-server Ar ip-address Oo , Ar ip-address ... Oc ; 549The 550.Ic smtp-server 551option specifies a list of SMTP servers available to the client. 552Servers should be listed in order of preference. 553.It Ic option static-routes Ar ip-address ip-address Oo , Ar ip-address ip-address ... Oc ; 554This option specifies a list of static routes that the client should 555install in its routing cache. 556If multiple routes to the same destination are specified, they are listed 557in descending order of priority. 558.Pp 559The routes consist of a list of IP address pairs. 560The first address is the destination address, 561and the second address is the router for the destination. 562.Pp 563The default route (0.0.0.0) is an illegal destination for a static route. 564To specify the default route, use the 565.Ic routers 566option. 567Note that this option is obsolete and should be replaced by the 568.Ic classless-static-routes 569option. 570.Xr dhclient 8 571ignores this option. 572.It Ic option streettalk-directory-assistance-server Ar ip-address Oo , Ar ip-address ... Oc ; 573The StreetTalk Directory Assistance (STDA) server option specifies a 574list of STDA servers available to the client. 575Servers should be listed in order of preference. 576.It Ic option streettalk-server Ar ip-address Oo , Ar ip-address ... Oc ; 577The 578.Ic streettalk-server 579option specifies a list of StreetTalk servers available to the client. 580Servers should be listed in order of preference. 581.It Ic option subnet-mask Ar ip-address ; 582The 583.Ic subnet-mask 584option specifies the client's subnet mask as per RFC 950. 585If no subnet-mask option is provided anywhere in scope, as a last resort 586.Xr dhcpd 8 587will use the subnet mask from the subnet declaration for the network on 588which an address is being assigned. 589However, 590.Em any 591subnet-mask option declaration that is in scope for the address being 592assigned will override the subnet mask specified in the subnet declaration. 593.It Ic option swap-server Ar ip-address ; 594This specifies the IP address of the client's swap server. 595.It Ic option tcp-keepalive-garbage Ar flag ; 596This option specifies whether or not the client should send TCP keepalive 597messages with an octet of garbage for compatibility with older implementations. 598A value of 0 indicates that a garbage octet should not be sent. 599A value of 1 indicates that a garbage octet should be sent. 600.It Ic option tcp-keepalive-interval Ar uint32 ; 601This option specifies the interval (in seconds) that the client TCP 602should wait before sending a keepalive message on a TCP connection. 603The time is specified as a 32-bit unsigned integer. 604A value of zero indicates that the client should not generate keepalive 605messages on connections unless specifically requested by an application. 606.It Ic option tftp-config-file Ar string ; 607Option 144. 608Per RFC 2132 options 128 \- 254 are site-specific. 609RFC 3942 reclassifies options 128 to 223 as publicly defined options and 610puts them in "Unavailable" state by IANA. 611See RFC 3679 for "Unused DHCP Option Codes to be Reassigned to Future 612DHCP Options". 613See RFC 2939 for procedures for definitions of new DHCP options. 614.It Ic option tftp-server-name Ar string ; 615This option is used to identify a TFTP server and, if supported by the 616client, should have the same effect as the 617.Ic server-name 618declaration. 619BOOTP clients are unlikely to support this option. 620Some DHCP clients will support it, and others actually require it. 621.It Ic option time-offset Ar int32 ; 622The 623.Ic time-offset 624option specifies the offset of the client's subnet in seconds from 625Coordinated Universal Time (UTC). 626.It Ic option time-servers Ar ip-address Oo , Ar ip-address ... Oc ; 627The 628.Ic time-server 629option specifies a list of RFC 868 time servers available to the client. 630Servers should be listed in order of preference. 631.It Ic option trailer-encapsulation Ar flag ; 632This option specifies whether or not the client should negotiate the 633use of trailers (RFC 893) when using the ARP protocol. 634A value of 0 indicates that the client should not attempt to use trailers. 635A value of 1 means that the client should attempt to use trailers. 636.It Ic option user-class Ar string ; 637This option is used by a DHCP client to optionally identify the type or 638category of user or applications it represents. 639A DHCP server uses the User Class option to choose the address pool it 640allocates an address from and/or to select any other configuration option. 641This option may carry multiple User Classes. 642Servers may interpret the meanings of multiple class specifications in an 643implementation dependent or configuration dependent manner, and so the use 644of multiple classes by a DHCP client should be based on the specific server 645implementation and configuration which will be used to process that User 646class option. 647See RFC 3004 for details. 648.It Ic option vendor-encapsulated-options Ar data-string ; 649This option is used by clients and servers to exchange vendor-specific 650information. 651The information is an opaque object of n octets, presumably interpreted by 652vendor-specific code on the clients and servers. 653See RFC 2132, Section 8.4 for details. 654.It Ic option voip-configuration-server Ar ip-address Oo , Ar ip-address ... Oc ; 655The 656.Ic voip-configuration-server 657option specifies a list of (normally TFTP) servers that VoIP clients 658may download their configuration information and software images 659from. 660Servers should be listed in order of preference. 661.It Ic option www-server Ar ip-address Oo , Ar ip-address ... Oc ; 662The 663.Ic www-server 664option specifies a list of WWW servers available to the client. 665.It Ic option x-display-manager Ar ip-address Oo , Ar ip-address ... Oc ; 666This option specifies a list of systems that are running the X Window 667System Display Manager and are available to the client. 668Addresses should be listed in order of preference. 669.El 670.Sh SEE ALSO 671.Xr dhclient.conf 5 , 672.Xr dhcpd.conf 5 , 673.Xr dhcpd.leases 5 , 674.Xr dhclient 8 , 675.Xr dhcpd 8 676.Sh STANDARDS 677.Rs 678.%A R. Droms 679.%D October 1993 680.%R RFC 1534 681.%T Interoperation Between DHCP and BOOTP 682.Re 683.Pp 684.Rs 685.%A R. Droms 686.%D March 1997 687.%R RFC 2131 688.%T Dynamic Host Configuration Protocol 689.Re 690.Pp 691.Rs 692.%A S. Alexander 693.%A R. Droms 694.%D March 1997 695.%R RFC 2132 696.%T DHCP Options and BOOTP Vendor Extensions 697.Re 698.Pp 699.Rs 700.%A T. Lemon 701.%A S. Cheshire 702.%D November 2002 703.%R RFC 3396 704.%T Encoding Long Options in the Dynamic Host Configuration Protocol (DHCPv4) 705.Re 706.Pp 707.Rs 708.%A T. Lemon 709.%A S. Cheshire 710.%A B. Volz 711.%D December 2002 712.%R RFC 3442 713.%T The Classless Static Route Option for Dynamic Host Configuration Protocol (DHCP) version 4 714.Re 715.Sh AUTHORS 716.An -nosplit 717.Xr dhcpd 8 718was written by 719.An Ted Lemon Aq Mt mellon@vix.com 720under a contract with Vixie Labs. 721.Pp 722The current implementation was reworked by 723.An Henning Brauer Aq Mt henning@openbsd.org . 724