1.\" $OpenBSD: dhcp-options.5,v 1.5 2005/03/02 15:30:42 jmc 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 January 1, 1995 40.Dt DHCP-OPTIONS 5 41.Os 42.Sh NAME 43.Nm dhcp-options 44.Nd Dynamic Host Configuration Protocol 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.Sh REFERENCE: OPTION STATEMENTS 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., 73.Li 239.254.197.10 ) 74or as a domain name (e.g., 75.Li haagen.isc.org ) . 76A domain name must resolve to a single IP address. 77.Pp 78The 79.Ar int32 80data type specifies a signed 32-bit integer. 81The 82.Ar uint32 83data type specifies an unsigned 32-bit integer. 84The 85.Ar int16 86and 87.Ar uint16 88data types specify signed and unsigned 16-bit integers. 89The 90.Ar int8 91and 92.Ar uint8 93data types specify signed and unsigned 8-bit integers. 94Unsigned 8-bit integers are also sometimes referred to as octets. 95.Pp 96The 97.Ar string 98data type specifies an 99.Tn NVT 100.Pq Network Virtual Terminal 101.Tn ASCII 102string, which must be enclosed in double quotes - for example, 103to specify a domain-name option, the syntax would be 104.Pp 105.Dl option domain-name \&"isc.org"; 106.Pp 107The 108.Ar flag 109data type specifies a boolean value. 110Booleans can be either 111.Li true 112or 113.Li false 114(or 115.Li on 116or 117.Li off , 118if that makes more sense to you). 119.Pp 120The 121.Ar data-string 122data type specifies either an 123.Tn NVT ASCII 124string enclosed in double quotes, or a series of octets specified in 125hexadecimal, separated by colons. 126For example: 127.Pp 128.Dl option dhcp-client-identifier \&"CLIENT-FOO"; 129or 130.Dl option dhcp-client-identifier 43:4c:49:45:54:2d:46:4f:4f; 131.Pp 132The documentation for the various options mentioned below is taken 133from the IETF draft document on DHCP options, RFC 2132. 134Options which are not listed by name may be defined by the name 135.Li option- Ns Ar nnn , 136where 137.Ar nnn 138is the decimal number of the option code. 139These options may be followed either by a string, enclosed in quotes, or by 140a series of octets, expressed as two-digit hexadecimal numbers separated 141by colons. 142For example: 143.Bd -literal -offset indent 144option option-133 "my-option-133-text"; 145option option-129 1:54:c9:2b:47; 146.Ed 147.Pp 148Because 149.Xr dhcpd 8 150does not know the format of these undefined option codes, 151no checking is done to ensure the correctness of the entered data. 152.Pp 153The standard options are: 154.Ss RFC 1497 Vendor Extensions 155.Bl -tag -width indent 156.It Ic option subnet-mask Ar ip-address ; 157The 158.Ic subnet-mask 159option specifies the client's subnet mask as per RFC 950. 160If no subnet-mask option is provided anywhere in scope, as a last resort 161.Xr dhcpd 8 162will use the subnet mask from the subnet declaration for the network on 163which an address is being assigned. 164However, 165.Em any 166subnet-mask option declaration that is in scope for the address being 167assigned will override the subnet mask specified in the subnet declaration. 168.It Ic option time-offset Ar int32 ; 169The 170.Ic time-offset 171option specifies the offset of the client's subnet in seconds from 172Coordinated Universal Time (UTC). 173.It Xo 174.Ic option routers Ar ip-address 175.Oo , Ar ip-address ... Oc ; 176.Xc 177The 178.Ic routers 179option specifies a list of IP addresses for routers on the client's subnet. 180Routers should be listed in order of preference. 181.It Xo 182.Ic option time-servers Ar ip-address 183.Oo , Ar ip-address ... Oc ; 184.Xc 185The 186.Ic time-server 187option specifies a list of RFC 868 time servers available to the client. 188Servers should be listed in order of preference. 189.It Xo 190.Ic option ien116-name-servers Ar ip-address 191.Oo , Ar ip-address ... Oc ; 192.Xc 193The 194.Ic ien116-name-servers 195option specifies a list of IEN 116 name servers available to the client. 196Servers should be listed in order of preference. 197.It Xo 198.Ic option domain-name-servers Ar ip-address 199.Oo , Ar ip-address ... Oc ; 200.Xc 201The 202.Ic domain-name-servers 203option specifies a list of Domain Name System (STD 13, RFC 1035) name servers 204available to the client. 205Servers should be listed in order of preference. 206.It Xo 207.Ic option log-servers Ar ip-address 208.Oo , Ar ip-address ... Oc ; 209.Xc 210The 211.Ic log-servers 212option specifies a list of MIT-LCS UDP log servers available to the client. 213Servers should be listed in order of preference. 214.It Xo 215.Ic option cookie-servers Ar ip-address 216.Oo , Ar ip-address ... Oc ; 217.Xc 218The 219.Ic cookie-servers 220option specifies a list of RFC 865 cookie servers available to the client. 221Servers should be listed in order of preference. 222.It Xo 223.Ic option lpr-servers Ar ip-address 224.Oo , Ar ip-address ... Oc ; 225.Xc 226The 227.Ic lpr-servers 228option specifies a list of RFC 1179 line printer servers available to the 229client. 230Servers should be listed in order of preference. 231.It Xo 232.Ic option impress-servers Ar ip-address 233.Oo , Ar ip-address ... Oc ; 234.Xc 235The 236.Ic impress-servers 237option specifies a list of Imagen Impress servers available to the client. 238Servers should be listed in order of preference. 239.It Xo 240.Ic option resource-location-servers Ar ip-address 241.Oo , Ar ip-address ... Oc ; 242.Xc 243This option specifies a list of RFC 887 Resource Location servers available 244to the client. 245Servers should be listed in order of preference. 246.It Ic option host-name Ar string ; 247This option specifies the name of the client. 248The name may or may not be qualified with the local domain name 249(it is preferable to use the 250.Ic domain-name 251option to specify the domain name). 252See RFC 1035 for character set restrictions. 253.It Ic option boot-size Ar uint16 ; 254This option specifies the length in 512-octet blocks of the default 255boot image for the client. 256.It Ic option merit-dump Ar string ; 257This option specifies the pathname of a file to which the client's 258core image should be dumped in the event the client crashes. 259The path is formatted as a character string consisting of characters from 260the 261.Tn NVT ASCII 262character set. 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-search Ar string ; 267This option specifies a list of domain names that the client should use 268when resolving hostnames via the Domain Name System. 269This option is defined in RFC 3397. 270.It Ic option swap-server Ar ip-address ; 271This specifies the IP address of the client's swap server. 272.It Ic option root-path Ar string ; 273This option specifies the pathname that contains the client's root disk. 274The path is formatted as a character string consisting of characters from 275the 276.Tn NVT ASCII 277character set. 278.El 279.Ss IP Layer Parameters per Host 280.Bl -tag -width indent 281.It Ic option ip-forwarding Ar flag ; 282This option specifies whether the client should configure its IP layer 283for packet forwarding. 284A value of 0 means disable IP forwarding, and a value of 1 means enable 285IP forwarding. 286.It Ic option non-local-source-routing Ar flag ; 287This option specifies whether the client should configure its IP 288layer to allow forwarding of datagrams with non-local source routes 289(see Section 3.3.5 of [4] for a discussion of this topic). 290A value of 0 means disallow forwarding of such datagrams, and a value of 1 291means allow forwarding. 292.It Xo 293.Ic option policy-filter Ar ip-address ip-address 294.Oo , Ar ip-address ip-address ... Oc ; 295.Xc 296This option specifies policy filters for non-local source routing. 297The filters consist of a list of IP addresses and masks which specify 298destination/mask pairs with which to filter incoming source routes. 299.Pp 300Any source-routed datagram whose next-hop address does not match one 301of the filters should be discarded by the client. 302.Pp 303See STD 3 (RFC 1122) for further information. 304.It Ic option max-dgram-reassembly Ar uint16 ; 305This option specifies the maximum size datagram that the client should be 306prepared to reassemble. 307The minimum legal value is 576. 308.It Ic option default-ip-ttl Ar uint8 ; 309This option specifies the default time-to-live that the client should 310use on outgoing datagrams. 311.It Ic option path-mtu-aging-timeout Ar uint32 ; 312This option specifies the timeout (in seconds) to use when aging Path 313MTU values discovered by the mechanism defined in RFC 1191. 314.It Xo 315.Ic option path-mtu-plateau-table Ar uint16 316.Oo , Ar uint16 ... Oc ; 317.Xc 318This option specifies a table of MTU sizes to use when performing 319Path MTU Discovery as defined in RFC 1191. 320The table is formatted as a list of 16-bit unsigned integers, 321ordered from smallest to largest. 322The minimum MTU value cannot be smaller than 68. 323.El 324.Ss IP Layer Parameters per Interface 325.Bl -tag -width indent 326.It Ic option interface-mtu Ar uint16 ; 327This option specifies the MTU to use on this interface. 328The minimum legal value for the MTU is 68. 329.It Ic option all-subnets-local Ar flag ; 330This option specifies whether or not the client may assume that all subnets 331of the IP network to which the client is connected use the same MTU as the 332subnet of that network to which the client is directly connected. 333A value of 1 indicates that all subnets share the same MTU. 334A value of 0 means that the client should assume that some subnets of the 335directly connected network may have smaller MTUs. 336.It Ic option broadcast-address Ar ip-address ; 337This option specifies the broadcast address in use on the client's subnet. 338Legal values for broadcast addresses are specified in section 3.2.1.3 of 339STD 3 (RFC 1122). 340.It Ic option perform-mask-discovery Ar flag ; 341This option specifies whether or not the client should perform subnet mask 342discovery using ICMP. 343A value of 0 indicates that the client should not perform mask discovery. 344A value of 1 means that the client should perform mask discovery. 345.It Ic option mask-supplier Ar flag ; 346This option specifies whether or not the client should respond to subnet mask 347requests using ICMP. 348A value of 0 indicates that the client should not respond. 349A value of 1 means that the client should respond. 350.It Ic option router-discovery Ar flag ; 351This option specifies whether or not the client should solicit routers using 352the Router Discovery mechanism defined in RFC 1256. 353A value of 0 indicates that the client should not perform router discovery. 354A value of 1 means that the client should perform router discovery. 355.It Ic option router-solicitation-address Ar ip-address ; 356This option specifies the address to which the client should transmit 357router solicitation requests. 358.It Xo 359.Ic option static-routes Ar ip-address ip-address 360.Oo , Ar ip-address ip-address ... Oc ; 361.Xc 362This option specifies a list of static routes that the client should 363install in its routing cache. 364If multiple routes to the same destination are specified, they are listed 365in descending order of priority. 366.Pp 367The routes consist of a list of IP address pairs. 368The first address is the destination address, 369and the second address is the router for the destination. 370.Pp 371The default route (0.0.0.0) is an illegal destination for a static route. 372To specify the default route, use the 373.Ic routers 374option. 375.El 376.Ss Link Layer Parameters per Interface 377.Bl -tag -width indent 378.It Ic option trailer-encapsulation Ar flag ; 379This option specifies whether or not the client should negotiate the 380use of trailers (RFC 893 [14]) when using the ARP protocol. 381A value of 0 indicates that the client should not attempt to use trailers. 382A value of 1 means that the client should attempt to use trailers. 383.It Ic option arp-cache-timeout Ar uint32 ; 384This option specifies the timeout in seconds for ARP cache entries. 385.It Ic option ieee802-3-encapsulation Ar flag ; 386This option specifies whether or not the client should use Ethernet 387Version 2 (RFC 894) or IEEE 802.3 (RFC 1042) encapsulation if the 388interface is an Ethernet. 389A value of 0 indicates that the client should use RFC 894 encapsulation. 390A value of 1 means that the client should use RFC 1042 encapsulation. 391.El 392.Ss TCP Parameters 393.Bl -tag -width indent 394.It Ic option default-tcp-ttl Ar uint8 ; 395This option specifies the default TTL that the client should use when 396sending TCP segments. 397The minimum value is 1. 398.It Ic option tcp-keepalive-interval Ar uint32 ; 399This option specifies the interval (in seconds) that the client TCP 400should wait before sending a keepalive message on a TCP connection. 401The time is specified as a 32-bit unsigned integer. 402A value of zero indicates that the client should not generate keepalive 403messages on connections unless specifically requested by an application. 404.It Ic option tcp-keepalive-garbage Ar flag ; 405This option specifies whether or not the client should send TCP keepalive 406messages with an octet of garbage for compatibility with older implementations. 407A value of 0 indicates that a garbage octet should not be sent. 408A value of 1 indicates that a garbage octet should be sent. 409.El 410.Ss Application and Service Parameters 411.Bl -tag -width indent 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 Xo 420.Ic option nis-servers Ar ip-address 421.Oo , Ar ip-address ... Oc ; 422.Xc 423This option specifies a list of IP addresses indicating NIS servers 424available to the client. 425Servers should be listed in order of preference. 426.It Xo 427.Ic option ntp-servers Ar ip-address 428.Oo , Ar ip-address ... Oc ; 429.Xc 430This option specifies a list of IP addresses indicating NTP (RFC 1305) 431servers available to the client. 432Servers should be listed in order of preference. 433.It Xo 434.Ic option netbios-name-servers Ar ip-address 435.Oo , Ar ip-address ... Oc ; 436.Xc 437The NetBIOS name server (NBNS) option specifies a list of RFC 1001/1002 438NBNS name servers listed in order of preference. 439NetBIOS Name Service is currently more commonly referred to as WINS. 440WINS servers can be specified using the 441.Ic netbios-name-servers 442option. 443.It Xo 444.Ic option netbios-dd-server Ar ip-address 445.Oo , Ar ip-address ... Oc ; 446.Xc 447The NetBIOS datagram distribution server (NBDD) option specifies a 448list of RFC 1001/1002 NBDD servers listed in order of preference. 449.It Ic option netbios-node-type Ar uint8 ; 450The NetBIOS node type option allows NetBIOS over TCP/IP clients which 451are configurable to be configured as described in RFC 1001/1002. 452The value is specified as a single octet which identifies the client type. 453.Pp 454Possible node types are: 455.Bl -tag -width indent 456.It 1 457B-node: Broadcast - no WINS 458.It 2 459P-node: Peer - WINS only 460.It 4 461M-node: Mixed - broadcast, then WINS 462.It 8 463H-node: Hybrid - WINS, then broadcast 464.El 465.It Ic option netbios-scope Ar string ; 466The NetBIOS scope option specifies the NetBIOS over TCP/IP scope 467parameter for the client as specified in RFC 1001/1002. 468See RFC 1001, RFC 1002, and RFC 1035 for character-set restrictions. 469.It Xo 470.Ic option font-servers Ar ip-address 471.Oo , Ar ip-address ... Oc ; 472.Xc 473This option specifies a list of X Window System Font servers available 474to the client. 475Servers should be listed in order of preference. 476.It Xo 477.Ic option x-display-manager Ar ip-address 478.Oo , Ar ip-address ... Oc ; 479.Xc 480This option specifies a list of systems that are running the X Window 481System Display Manager and are available to the client. 482Addresses should be listed in order of preference. 483.It Ic option dhcp-client-identifier Ar data-string ; 484This option can be used to specify a DHCP client identifier in a 485host declaration, so that 486.Xr dhcpd 8 487can find the host record by matching against the client identifier. 488.It Ic option nisplus-domain Ar string ; 489This option specifies the name of the client's NIS+ domain. 490The domain is formatted as a character string consisting of characters 491from the 492.Tn NVT ASCII 493character set. 494.It Xo 495.Ic option nisplus-servers Ar ip-address 496.Oo , Ar ip-address ... Oc ; 497.Xc 498This option specifies a list of IP addresses indicating NIS+ servers 499available to the client. 500Servers should be listed in order of preference. 501.It Ic option tftp-server-name Ar string ; 502This option is used to identify a TFTP server and, if supported by the 503client, should have the same effect as the 504.Ic server-name 505declaration. 506BOOTP clients are unlikely to support this option. 507Some DHCP clients will support it, and others actually require it. 508.It Ic option bootfile-name Ar string ; 509This option is used to identify a bootstrap file. 510If supported by the client, it should have the same effect as the 511.Ic filename 512declaration. 513BOOTP clients are unlikely to support this option. 514Some DHCP clients will support it, and others actually require it. 515.It Xo 516.Ic option mobile-ip-home-agent Ar ip-address 517.Oo , Ar ip-address ... Oc ; 518.Xc 519This option specifies a list of IP addresses indicating mobile IP 520home agents available to the client. 521Agents should be listed in order of preference, although normally there 522will be only one such agent. 523.It Xo 524.Ic option smtp-server Ar ip-address 525.Oo , Ar ip-address ... Oc ; 526.Xc 527The 528.Ic smtp-server 529option specifies a list of SMTP servers available to the client. 530Servers should be listed in order of preference. 531.It Xo 532.Ic option pop-server Ar ip-address 533.Oo , Ar ip-address ... Oc ; 534.Xc 535The 536.Ic pop-server 537option specifies a list of POP3 servers available to the client. 538Servers should be listed in order of preference. 539.It Xo 540.Ic option nntp-server Ar ip-address 541.Oo , Ar ip-address ... Oc ; 542.Xc 543The 544.Ic nntp-server 545option specifies a list of NNTP servers available to the client. 546Servers should be listed in order of preference. 547.It Xo 548.Ic option www-server Ar ip-address 549.Oo , Ar ip-address ... Oc ; 550.Xc 551The 552.Ic www-server 553option specifies a list of WWW servers available to the client. 554Servers should be listed in order of preference. 555.It Xo 556.Ic option finger-server Ar ip-address 557.Oo , Ar ip-address ... Oc ; 558.Xc 559The 560.Ic finger-server 561option specifies a list of 562.Xr finger 1 563servers available to the client. 564Servers should be listed in order of preference. 565.It Xo 566.Ic option irc-server Ar ip-address 567.Oo , Ar ip-address ... Oc ; 568.Xc 569The 570.Ic irc-server 571option specifies a list of IRC servers available to the client. 572Servers should be listed in order of preference. 573.It Xo 574.Ic option streettalk-server Ar ip-address 575.Oo , Ar ip-address ... Oc ; 576.Xc 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 Xo 582.Ic option streettalk-directory-assistance-server Ar ip-address 583.Oo , Ar ip-address ... Oc ; 584.Xc 585The StreetTalk Directory Assistance (STDA) server option specifies a 586list of STDA servers available to the client. 587Servers should be listed in order of preference. 588.It Ic option url Ar string ; 589This option specifies the URL that the client may use when using UEFI 590boot from a HTTP server. 591.El 592.Sh SEE ALSO 593.Xr dhclient.conf 5 , 594.Xr dhcpd.conf 5 , 595.Xr dhcpd.leases 5 , 596.Xr dhclient 8 , 597.Xr dhcpd 8 598.Rs 599.%R "RFC 2131, RFC 2132, RFC 3769" 600.Re 601.Sh AUTHORS 602.An -nosplit 603The 604.Xr dhcpd 8 605utility 606was written by 607.An Ted Lemon Aq Mt mellon@vix.com 608under a contract with Vixie Labs. 609.Pp 610The current implementation was reworked by 611.An Henning Brauer Aq Mt henning@openbsd.org . 612