1.\" $OpenBSD: dhcpd.conf.5,v 1.10 2009/09/01 08:42:31 reyk Exp $ 2.\" 3.\" Copyright (c) 1995, 1996, 1997, 1998, 1998, 1999 4.\" The Internet Software Consortium. 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 1 2009 $ 40.Dt DHCPD.CONF 5 41.Os 42.Sh NAME 43.Nm dhcpd.conf 44.Nd dhcpd configuration file 45.Sh DESCRIPTION 46The 47.Nm 48file contains configuration information for 49.Xr dhcpd 8 , 50the Internet Software Consortium DHCP Server. 51.Pp 52The 53.Nm 54file is a free-form ASCII text file. 55It is parsed by the recursive-descent parser built into 56.Xr dhcpd 8 . 57The file may contain extra tabs and newlines for formatting purposes. 58Keywords in the file are case-insensitive. 59Comments may be placed anywhere within the file (except within quotes). 60Comments begin with the 61.Sq # 62character and end at the end of the line. 63.Pp 64The file essentially consists of a list of statements. 65Statements fall into two broad categories \- parameters and declarations. 66.Pp 67Parameter statements say how to do something (e.g., how long a 68lease to offer), whether to do something (e.g., should 69.Xr dhcpd 8 70provide addresses to unknown clients), or what parameters to provide to the 71client (e.g., use gateway 220.177.244.7). 72.Pp 73Declarations are used to describe the topology of the 74network, to describe clients on the network, to provide addresses that 75can be assigned to clients, or to apply a group of parameters to a 76group of declarations. 77In any group of parameters and declarations, all parameters must be specified 78before any declarations which depend on those parameters may be specified. 79.Pp 80Declarations about network topology include the 81.Ic shared-network 82and the 83.Ic subnet 84declarations. 85If clients on a subnet are to be assigned addresses dynamically, a 86.Ic range 87declaration must appear within the 88.Ic subnet 89declaration. 90For clients with statically assigned addresses, or for installations where 91only known clients will be served, each such client must have a 92.Ic host 93declaration. 94If parameters are to be applied to a group of declarations which are not 95related strictly on a per-subnet basis, the 96.Ic group 97declaration can be used. 98.Pp 99For every subnet which will be served, and for every subnet 100to which the dhcp server is connected, there must be one 101.Ic subnet 102declaration, which tells 103.Xr dhcpd 8 104how to recognize that an address is on that subnet. 105A 106.Ic subnet 107declaration is required for each subnet even if no addresses will be 108dynamically allocated on that subnet. 109.Pp 110Some installations have physical networks on which more than one IP 111subnet operates. 112For example, if there is a site-wide requirement that 8-bit subnet masks 113be used, but a department with a single physical Ethernet network expands 114to the point where it has more than 254 nodes, it may be necessary to run 115two 8-bit subnets on the same Ethernet until such time as a new physical 116network can be added. 117In this case, the 118.Ic subnet 119declarations for these two networks may be enclosed in a 120.Ic shared-network 121declaration. 122.Pp 123Some sites may have departments which have clients on more than one 124subnet, but it may be desirable to offer those clients a uniform set 125of parameters which are different than what would be offered to 126clients from other departments on the same subnet. 127For clients which will be declared explicitly with 128.Ic host 129declarations, these declarations can be enclosed in a 130.Ic group 131declaration along with the parameters which are common to that department. 132For clients whose addresses will be dynamically assigned, there is currently no 133way to group parameter assignments other than by network topology. 134.Pp 135When a client is to be booted, its boot parameters are determined by 136first consulting that client's 137.Ic host 138declaration (if any), then consulting the 139.Ic group 140declaration (if any) which enclosed that 141.Ic host 142declaration, then consulting the 143.Ic subnet 144declaration for the subnet on which the client is booting, then consulting the 145.Ic shared-network 146declaration (if any) containing that subnet, and finally consulting the 147top-level parameters which may be specified outside of any declaration. 148.Pp 149When 150.Xr dhcpd 8 151tries to find a 152.Ic host 153declaration for a client, it first looks for a 154.Ic host 155declaration which has a 156.Ar fixed-address 157parameter which matches the subnet or shared network on which the client 158is booting. 159If it doesn't find any such entry, it then tries to find an entry which has no 160.Ar fixed-address 161parameter. 162If no such entry is found, then 163.Xr dhcpd 8 164acts as if there is no entry in the 165.Nm 166file for that client, even if there is an entry for that client on a 167different subnet or shared network. 168.Sh EXAMPLES 169A typical 170.Nm 171file will look something like this: 172.Pp 173Example 1 174.Bd -unfilled -offset indent 175.Ar global parameters... 176 177shared-network ISC-BIGGIE { 178.Ar \ \&\ \&shared-network-specific parameters... 179 subnet 204.254.239.0 netmask 255.255.255.224 { 180.Ar \ \&\ \&\ \&\ \&subnet-specific parameters... 181 range 204.254.239.10 204.254.239.30; 182 } 183 subnet 204.254.239.32 netmask 255.255.255.224 { 184.Ar \ \&\ \&\ \&\ \&subnet-specific parameters... 185 range 204.254.239.42 204.254.239.62; 186 } 187} 188 189subnet 204.254.239.64 netmask 255.255.255.224 { 190.Ar \ \&\ \&subnet-specific parameters... 191 range 204.254.239.74 204.254.239.94; 192} 193 194group { 195.Ar \ \&\ \&group-specific parameters... 196 host zappo.test.isc.org { 197.Ar \ \&\ \&\ \&\ \&host-specific parameters... 198 } 199 host beppo.test.isc.org { 200.Ar \ \&\ \&\ \&\ \&host-specific parameters... 201 } 202 host harpo.test.isc.org { 203.Ar \ \&\ \&\ \&\ \&host-specific parameters... 204 } 205} 206.Ed 207.Pp 208Notice that at the beginning of the file, there's a place 209for global parameters. 210These might be things like the organization's domain name, 211the addresses of the name servers 212(if they are common to the entire organization), and so on. 213So, for example: 214.Pp 215Example 2 216.Bd -literal -offset indent 217option domain-name \&"isc.org\&"; 218option domain-name-servers ns1.isc.org, ns2.isc.org; 219.Ed 220.Pp 221As you can see in Example 2, it's legal to specify host addresses in 222parameters as domain names rather than as numeric IP addresses. 223If a given hostname resolves to more than one IP address (for example, if 224that host has two Ethernet interfaces), both addresses are supplied to 225the client. 226.Pp 227In Example 1, you can see that both the shared-network statement and 228the subnet statements can have parameters. 229Let us say that the shared network ISC-BIGGIE supports an entire department \- 230perhaps the accounting department. 231If accounting has its own domain, then a shared-network-specific parameter 232might be: 233.Pp 234.Dl option domain-name \&"accounting.isc.org\&"; 235.Pp 236All subnet declarations appearing in the shared-network declaration 237would then have the domain-name option set to 238.Dq accounting.isc.org 239instead of just 240.Dq isc.org . 241.Pp 242The most obvious reason for having subnet-specific parameters as 243shown in Example 1 is that each subnet, of necessity, has its own router. 244So for the first subnet, for example, there should be something like: 245.Pp 246.Dl option routers 204.254.239.1; 247.Pp 248Note that the address here is specified numerically. 249This is not required \- if you have a different domain name for each 250interface on your router, it's perfectly legitimate to use the domain name 251for that interface instead of the numeric address. 252However, in many cases there may be only one domain name for all of a router's 253IP addresses, and it would not be appropriate to use that name here. 254.Pp 255In Example 1 there is also a 256.Ic group 257statement, which provides common parameters for a set of three hosts \- zappo, 258beppo and harpo. 259As you can see, these hosts are all in the test.isc.org domain, so it 260might make sense for a group-specific parameter to override the domain 261name supplied to these hosts: 262.Pp 263.Dl option domain-name \&"test.isc.org\&"; 264.Pp 265Also, given the domain they're in, these are probably test machines. 266If we wanted to test the DHCP leasing mechanism, we might set the 267lease timeout somewhat shorter than the default: 268.Bd -literal -offset indent 269max-lease-time 120; 270default-lease-time 120; 271.Ed 272.Pp 273You may have noticed that while some parameters start with the 274.Ic option 275keyword, some do not. 276Parameters starting with the 277.Ic option 278keyword correspond to actual DHCP options, while parameters that do not start 279with the option keyword either control the behaviour of the DHCP server 280(e.g., how long a lease 281.Xr dhcpd 8 282will give out), or specify client parameters that are not optional in the 283DHCP protocol (for example, server-name and filename). 284.Pp 285In Example 1, each host had 286.Ar host-specific parameters . 287These could include such things as the 288.Ic hostname 289option, the name of a file to download (the 290.Ar filename 291parameter) and the address of the server from which to download the file (the 292.Ar next-server 293parameter). 294In general, any parameter can appear anywhere that parameters are allowed, 295and will be applied according to the scope in which the parameter appears. 296.Pp 297Imagine that you have a site with a lot of NCD X-Terminals. 298These terminals come in a variety of models, and you want to specify the 299boot files for each model. 300One way to do this would be to have host declarations for each server 301and group them by model: 302.Bd -literal -offset indent 303group { 304 filename "Xncd19r"; 305 next-server ncd-booter; 306 307 host ncd1 { hardware ethernet 0:c0:c3:49:2b:57; } 308 host ncd4 { hardware ethernet 0:c0:c3:80:fc:32; } 309 host ncd8 { hardware ethernet 0:c0:c3:22:46:81; } 310} 311 312group { 313 filename "Xncd19c"; 314 next-server ncd-booter; 315 316 host ncd2 { hardware ethernet 0:c0:c3:88:2d:81; } 317 host ncd3 { hardware ethernet 0:c0:c3:00:14:11; } 318} 319 320group { 321 filename "XncdHMX"; 322 next-server ncd-booter; 323 324 host ncd5 { hardware ethernet 0:c0:c3:11:90:23; } 325 host ncd6 { hardware ethernet 0:c0:c3:91:a7:8; } 326 host ncd7 { hardware ethernet 0:c0:c3:cc:a:8f; } 327} 328.Ed 329.Sh REFERENCE: DECLARATIONS 330The 331.Ic shared-network 332statement 333.Bd -unfilled -offset indent 334.Ic shared-network Ar name No { 335.Pf \ \&\ \& Op Ar parameters 336.Pf \ \&\ \& Op Ar declarations 337} 338.Ed 339.Pp 340The 341.Ic shared-network 342statement is used to inform the DHCP server that some IP subnets actually 343share the same physical network. 344Any subnets in a shared network should be declared within a 345.Ic shared-network 346statement. 347Parameters specified in the 348.Ic shared-network 349statement will be used when booting clients on those subnets unless 350parameters provided at the subnet or host level override them. 351If any subnet in a shared network has addresses available for dynamic 352allocation, those addresses are collected into a common pool for that 353shared network and assigned to clients as needed. 354There is no way to distinguish on which subnet of a shared network a 355client should boot. 356.Pp 357.Ar name 358should be the name of the shared network. 359This name is used when printing debugging messages, so it should be 360descriptive for the shared network. 361The name may have the syntax of a valid domain name 362(although it will never be used as such), or it may be any arbitrary 363name, enclosed in quotes. 364.Pp 365The 366.Ic subnet 367statement 368.Bd -unfilled -offset indent 369.Ic subnet Ar subnet-number Ic netmask Ar netmask No { 370.Pf \ \&\ \& Op Ar parameters 371.Pf \ \&\ \& Op Ar declarations 372} 373.Ed 374.Pp 375The 376.Ic subnet 377statement is used to provide 378.Xr dhcpd 8 379with enough information to tell whether or not an IP address is on that subnet. 380It may also be used to provide subnet-specific parameters and to 381specify what addresses may be dynamically allocated to clients booting 382on that subnet. 383Such addresses are specified using the 384.Ic range 385declaration. 386.Pp 387The 388.Ar subnet-number 389and 390.Ar netmask 391should be specified as numeric IP addresses. 392The subnet number, together with the netmask, are sufficient to determine 393whether any given IP address is on the specified subnet. 394.Pp 395Although a netmask must be given with every subnet declaration, it is 396recommended that if there is any variance in subnet masks at a site, a 397subnet-mask option statement be used in each subnet declaration to set 398the desired subnet mask, since any subnet-mask option statement will 399override the subnet mask declared in the subnet statement. 400.Pp 401The 402.Ic range 403statement 404.Pp 405.Xo 406.Ic range Op Ic dynamic-bootp 407.Ar low-address Oo Ar high-address Oc ; 408.Xc 409.Pp 410For any subnet on which addresses will be assigned dynamically, there 411must be at least one 412.Ic range 413statement. 414The range statement gives the lowest and highest IP addresses in a range. 415All IP addresses in the range should be in the subnet in which the 416.Ic range 417statement is declared. 418The 419.Ic dynamic-bootp 420flag may be specified if addresses in the specified range may be dynamically 421assigned to BOOTP clients as well as DHCP clients. 422When specifying a single address, 423.Ar high-address 424can be omitted. 425.Pp 426The 427.Ic host 428statement 429.Bd -unfilled -offset indent 430.Ic host Ar hostname No { 431.Pf \ \&\ \& Op Ar parameters 432.Pf \ \&\ \& Op Ar declarations 433} 434.Ed 435.Pp 436There must be at least one 437.Ic host 438statement for every BOOTP client that is to be served. 439.Ic host 440statements may also be specified for DHCP clients, although this is 441not required unless booting is only enabled for known hosts. 442.Pp 443If it is desirable to be able to boot a DHCP or BOOTP 444client on more than one subnet with fixed addresses, more than one 445address may be specified in the 446.Ar fixed-address 447parameter, or more than one 448.Ic host 449statement may be specified. 450.Pp 451If client-specific boot parameters must change based on the network 452to which the client is attached, then multiple 453.Ic host 454statements should be used. 455.Pp 456If a client is to be booted using a fixed address if it's 457possible, but should be allocated a dynamic address otherwise, then a 458.Ic host 459statement must be specified without a 460.Ar fixed-address 461clause. 462.Ar hostname 463should be a name identifying the host. 464If a 465.Ar hostname 466option is not specified for the host, 467.Ar hostname 468is used. 469.Pp 470.Ic host 471declarations are matched to actual DHCP or BOOTP clients by matching the 472.Ic dhcp-client-identifier 473option specified in the 474.Ic host 475declaration to the one supplied by the client, or, if the 476.Ic host 477declaration or the client does not provide a 478.Ic dhcp-client-identifier 479option, by matching the 480.Ar hardware 481parameter in the 482.Ic host 483declaration to the network hardware address supplied by the client. 484BOOTP clients do not normally provide a 485.Ar dhcp-client-identifier , 486so the hardware address must be used for all clients that may boot using 487the BOOTP protocol. 488.Pp 489The 490.Ic group 491statement 492.Bd -unfilled -offset indent 493.Ic group No { 494.Pf \ \&\ \& Op Ar parameters 495.Pf \ \&\ \& Op Ar declarations 496} 497.Ed 498.Pp 499The 500.Ic group 501statement is used simply to apply one or more parameters to a group of 502declarations. 503It can be used to group hosts, shared networks, subnets, or even other groups. 504.Sh REFERENCE: ALLOW and DENY 505The 506.Ic allow 507and 508.Ic deny 509statements can be used to control the behaviour of 510.Xr dhcpd 8 511to various sorts of requests. 512.Pp 513The 514.Ar unknown-clients 515keyword 516.Bd -literal -offset indent 517allow unknown-clients; 518deny unknown-clients; 519.Ed 520.Pp 521The 522.Ar unknown-clients 523flag is used to tell 524.Xr dhcpd 8 525whether or not to dynamically assign addresses to unknown clients. 526Dynamic address assignment to unknown clients is allowed by default. 527.Pp 528The 529.Ar bootp 530keyword 531.Bd -literal -offset indent 532allow bootp; 533deny bootp; 534.Ed 535.Pp 536The 537.Ar bootp 538flag is used to tell 539.Xr dhcpd 8 540whether or not to respond to bootp queries. 541Bootp queries are allowed by default. 542.Pp 543The 544.Ar booting 545keyword 546.Bd -literal -offset indent 547allow booting; 548deny booting; 549.Ed 550.Pp 551The 552.Ar booting 553flag is used to tell 554.Xr dhcpd 8 555whether or not to respond to queries from a particular client. 556This keyword only has meaning when it appears in a host declaration. 557By default, booting is allowed, but if it is disabled for a particular client, 558then that client will not be able to get an address from the DHCP server. 559.Sh REFERENCE: PARAMETERS 560The 561.Ic default-lease-time 562statement 563.Pp 564.D1 Ic default-lease-time Ar time ; 565.Pp 566.Ar time 567should be the length in seconds that will be assigned to a lease if 568the client requesting the lease does not ask for a specific expiration time. 569.Pp 570The 571.Ic max-lease-time 572statement 573.Pp 574.D1 Ic max-lease-time Ar time ; 575.Pp 576.Ar time 577should be the maximum length in seconds that will be assigned to a 578lease if the client requesting the lease asks for a specific expiration time. 579.Pp 580The 581.Ic hardware 582statement 583.Pp 584.D1 Ic hardware Ar hardware-type hardware-address ; 585.Pp 586In order for a BOOTP client to be recognized, its network hardware 587address must be declared using a 588.Ic hardware 589clause in the 590.Ic host 591statement. 592.Ar hardware-type 593must be the name of a hardware interface type. 594Currently, the 595.Ar ethernet , 596.Ar token-ring 597and 598.Ar fddi 599physical interface types are recognized, 600although support for DHCP-over-IPSec virtual interface type 601.Ar ipsec-tunnel 602is provided. 603The 604.Ar hardware-address 605should be a set of hexadecimal octets (numbers from 0 through ff) 606separated by colons. 607The 608.Ic hardware 609statement may also be used for DHCP clients. 610.Pp 611The 612.Ic filename 613statement 614.Pp 615.D1 Ic filename Ar \&"filename\&" ; 616.Pp 617The 618.Ic filename 619statement can be used to specify the name of the initial boot file which 620is to be loaded by a client. 621The 622.Ar filename 623should be a filename recognizable to whatever file transfer protocol 624the client can be expected to use to load the file. 625.Pp 626The 627.Ic server-name 628statement 629.Pp 630.D1 Ic server-name Ar \&"name\&" ; 631.Pp 632The 633.Ic server-name 634statement can be used to inform the client of the name of the server 635from which it is booting. 636.Ar name 637should be the name that will be provided to the client. 638.Pp 639The 640.Ic next-server 641statement 642.Pp 643.D1 Ic next-server Ar server-name ; 644.Pp 645The 646.Ic next-server 647statement is used to specify the host address of 648the server from which the initial boot file (specified in the 649.Ic filename 650statement) is to be loaded. 651.Ar server-name 652should be a numeric IP address or a domain name. 653If no 654.Ic next-server 655parameter applies to a given client, the DHCP server's IP address is used. 656.Pp 657The 658.Ic fixed-address 659statement 660.Pp 661.Xo 662.Ic \ \&fixed-address Ar address 663.Op , Ar address ... ; 664.Xc 665.Pp 666The 667.Ic fixed-address 668statement is used to assign one or more fixed IP addresses to a client. 669It should only appear in a 670.Ic host 671declaration. 672If more than one address is supplied, then when the client boots, it will be 673assigned the address which corresponds to the network on which it is booting. 674If none of the addresses in the 675.Ic fixed-address 676statement are on the network on which the client is booting, that client will 677not match the 678.Ic host 679declaration containing that 680.Ic fixed-address 681statement. 682Each 683.Ar address 684should be either an IP address or a domain name which resolves to one 685or more IP addresses. 686.Pp 687Clients with fixed addresses are not assigned DHCP leases, 688and may therefore not be used with the 689.Fl ACL 690table options of 691.Xr dhcpd 8 . 692.Pp 693The 694.Ic dynamic-bootp-lease-cutoff 695statement 696.Pp 697.D1 Ic dynamic-bootp-lease-cutoff Ar date ; 698.Pp 699The 700.Ic dynamic-bootp-lease-cutoff 701statement sets the ending time for all leases assigned dynamically to 702BOOTP clients. 703Because BOOTP clients do not have any way of renewing leases, 704and don't know that their leases could expire, by default 705.Xr dhcpd 8 706assigns infinite leases to all BOOTP clients. 707However, it may make sense in some situations to set a cutoff date for all 708BOOTP leases \- for example, the end of a school term, 709or the time at night when a facility is closed and all 710machines are required to be powered off. 711.Pp 712.Ar date 713should be the date on which all assigned BOOTP leases will end. 714The date is specified in the form: 715.Pp 716.Dl W YYYY/MM/DD HH:MM:SS 717.Pp 718W is the day of the week expressed as a number from zero (Sunday) 719to six (Saturday). 720YYYY is the year, including the century. 721MM is the month expressed as a number from 1 to 12. 722DD is the day of the month, counting from 1. 723HH is the hour, from zero to 23. 724MM is the minute and SS is the second. 725The time is always in Coordinated Universal Time (UTC), not local time. 726.Pp 727The 728.Ic dynamic-bootp-lease-length 729statement 730.Pp 731.D1 Ic dynamic-bootp-lease-length Ar length ; 732.Pp 733The 734.Ic dynamic-bootp-lease-length 735statement is used to set the length of leases dynamically assigned to 736BOOTP clients. 737At some sites, it may be possible to assume that a lease is no longer in 738use if its holder has not used BOOTP or DHCP to get its address within 739a certain time period. 740The period is specified in 741.Ar length 742as a number of seconds. 743If a client reboots using BOOTP during the timeout period, the lease 744duration is reset to 745.Ar length , 746so a BOOTP client that boots frequently enough will never lose its lease. 747Needless to say, this parameter should be adjusted with extreme caution. 748.Pp 749The 750.Ic get-lease-hostnames 751statement 752.Pp 753.D1 Ic get-lease-hostnames Ar flag ; 754.Pp 755The 756.Ic get-lease-hostnames 757statement is used to tell 758.Xr dhcpd 8 759whether or not to look up the domain name corresponding to the IP address of 760each address in the lease pool and use that address for the DHCP 761.Ic hostname 762option. 763If 764.Ar flag 765is true, then this lookup is done for all addresses in the current scope. 766By default, or if 767.Ar flag 768is false, no lookups are done. 769.Pp 770The 771.Ic use-host-decl-names 772statement 773.Pp 774.D1 Ic use-host-decl-names Ar flag ; 775.Pp 776If the 777.Ic use-host-decl-names 778parameter is true in a given scope, then for every host declaration within 779that scope, the name provided for the host declaration will be supplied to 780the client as its hostname. 781So, for example, 782.Bd -literal -offset indent 783group { 784 use-host-decl-names on; 785 786 host joe { 787 hardware ethernet 08:00:2b:4c:29:32; 788 fixed-address joe.fugue.com; 789 } 790} 791.Ed 792.Pp 793is equivalent to 794.Bd -literal -offset indent 795host joe { 796 hardware ethernet 08:00:2b:4c:29:32; 797 fixed-address joe.fugue.com; 798 option host-name "joe"; 799} 800.Ed 801.Pp 802An 803.Ic option host-name 804statement within a host declaration will override the use of the name 805in the host declaration. 806.Pp 807The 808.Ic authoritative 809statement 810.Pp 811.D1 Ic authoritative ; 812.Pp 813.D1 Ic not authoritative ; 814.Pp 815The DHCP server will normally assume that the configuration 816information about a given network segment is known to be correct and 817is authoritative. 818So if a client requests an IP address on a given network segment that the 819server knows is not valid for that segment, the server will respond with a 820DHCPNAK message, causing the client to forget its IP address and try to get 821a new one. 822.Pp 823If a DHCP server is being configured by somebody who is not the 824network administrator and who therefore does not wish to assert this 825level of authority, then the statement 826.Dq not authoritative 827should be written in the appropriate scope in the configuration file. 828.Pp 829Usually, writing 830.Em not authoritative; 831at the top level of the file should be sufficient. 832However, if a DHCP server is to be set up so that it is aware of some 833networks for which it is authoritative and some networks for which it is not, 834it may be more appropriate to declare authority on a per-network-segment basis. 835.Pp 836Note that the most specific scope for which the concept of authority 837makes any sense is the physical network segment \- either a 838shared-network statement or a subnet statement that is not contained 839within a shared-network statement. 840It is not meaningful to specify that the server is authoritative for some 841subnets within a shared network, but not authoritative for others, 842nor is it meaningful to specify that the server is authoritative for some 843host declarations and not others. 844.Pp 845The 846.Ic use-lease-addr-for-default-route 847statement 848.Pp 849.D1 Ic use-lease-addr-for-default-route Ar flag ; 850.Pp 851If the 852.Ic use-lease-addr-for-default-route 853parameter is true in a given scope, then instead of sending the value 854specified in the routers option (or sending no value at all), 855the IP address of the lease being assigned is sent to the client. 856This supposedly causes Win95 machines to ARP for all IP addresses, 857which can be helpful if your router is configured for proxy ARP. 858.Pp 859If 860.Ic use-lease-addr-for-default-route 861is enabled and an option routers statement are both in scope, 862the routers option will be preferred. 863The rationale for this is that in situations where you want to use 864this feature, you probably want it enabled for a whole bunch of 865Windows 95 machines, and you want to override it for a few other machines. 866Unfortunately, if the opposite happens to be true for your 867site, you are probably better off not trying to use this flag. 868.Pp 869The 870.Ic always-reply-rfc1048 871statement 872.Pp 873.D1 Ic always-reply-rfc1048 Ar flag ; 874.Pp 875Some BOOTP clients expect RFC 1048-style responses, but do not follow 876RFC 1048 when sending their requests. 877You can tell that a client is having this problem if it is not getting 878the options you have configured for it and if you see in the server log 879the message 880.Dq (non-rfc1048) 881printed with each BOOTREQUEST that is logged. 882.Pp 883If you want to send RFC 1048 options to such a client, you can set the 884.Ic always-reply-rfc1048 885option in that client's host declaration, and the DHCP server will 886respond with an RFC 1048-style vendor options field. 887This flag can be set in any scope, and will affect all clients covered 888by that scope. 889.Pp 890The 891.Ic server-identifier 892statement 893.Pp 894.D1 Ic server-identifier Ar hostname ; 895.Pp 896The 897.Ic server-identifier 898statement can be used to define the value that is sent in the 899DHCP Server Identifier option for a given scope. 900The value specified 901.Em must 902be an IP address for the DHCP server, and must be reachable by all 903clients served by a particular scope. 904.Pp 905The use of the server-identifier statement is not recommended \- the only 906reason to use it is to force a value other than the default value to be 907sent on occasions where the default value would be incorrect. 908The default value is the first IP address associated with the physical 909network interface on which the request arrived. 910.Pp 911The usual case where the 912.Ic server-identifier 913statement needs to be sent is when a physical interface has more than one 914IP address, and the one being sent by default isn't appropriate for some 915or all clients served by that interface. 916Another common case is when an alias is defined for the purpose of 917having a consistent IP address for the DHCP server, and it is desired 918that the clients use this IP address when contacting the server. 919.Pp 920Supplying a value for the 921.Ic dhcp-server-identifier 922option is equivalent to using the 923.Ic server-identifier 924statement. 925.Sh REFERENCE: OPTION STATEMENTS 926DHCP option statements are documented in the 927.Xr dhcp-options 5 928manual page. 929.Sh SEE ALSO 930.Xr dhcp-options 5 , 931.Xr dhcpd.leases 5 , 932.Xr dhcpd 8 933.Pp 934RFC 2132, RFC 2131, RFC 3046, RFC 3456 935.Sh AUTHORS 936.An -nosplit 937.Xr dhcpd 8 938was written by 939.An Ted Lemon Aq mellon@vix.com 940under a contract with Vixie Labs. 941.Pp 942The current implementation was reworked by 943.An Henning Brauer Aq henning@openbsd.org . 944