.\" dhcp-options.5 .\" .\" Copyright (c) 1996-1999 Internet Software Consortium. .\" Use is subject to license terms which appear in the file named .\" ISC-LICENSE that should have accompanied this file when you .\" received it. If a file named ISC-LICENSE did not accompany this .\" file, or you are not sure the one you have is correct, you may .\" obtain an applicable copy of the license at: .\" .\" http://www.isc.org/isc-license-1.0.html. .\" .\" This file is part of the ISC DHCP distribution. The documentation .\" associated with this file is listed in the file DOCUMENTATION, .\" included in the top-level directory of this release. .\" .\" Support and other services are available for ISC products - see .\" http://www.isc.org for more information. .TH dhcpd-options 5 .SH NAME dhcp-options - Dynamic Host Configuration Protocol options .SH DESCRIPTION The Dynamic Host Configuration protocol allows the client to receive .B options from the DHCP server describing the network configuration and various services that are available on the network. When configuring .B dhcpd(8) or .B dhclient(8) , options must often be declared. The syntax for declaring options, and the names and formats of the options that can be declared, are documented here. .SH REFERENCE: OPTION STATEMENTS .PP DHCP \fIoption\fR statements always start with the \fIoption\fR keyword, followed by an option name, followed by option data. The option names and data formats are described below. It is not necessary to exhaustively specify all DHCP options - only those options which are needed by clients must be specified. .PP Option data comes in a variety of formats, as defined below: .PP The .B ip-address data type can be entered either as an explicit IP address (e.g., 239.254.197.10) or as a domain name (e.g., haagen.isc.org). When entering a domain name, be sure that that domain name resolves to a single IP address. .PP The .B int32 data type specifies a signed 32-bit integer. The .B uint32 data type specifies an unsigned 32-bit integer. The .B int16 and .B uint16 data types specify signed and unsigned 16-bit integers. The .B int8 and .B uint8 data types specify signed and unsigned 8-bit integers. Unsigned 8-bit integers are also sometimes referred to as octets. .PP The .B text data type specifies an NVT ASCII string, which must be enclosed in double quotes - for example, to specify a domain-name option, the syntax would be .nf .sp 1 option domain-name "isc.org"; .fi .PP The .B flag data type specifies a boolean value. Booleans can be either true or false (or on or off, if that makes more sense to you). .PP The .B string data type specifies either an NVT ASCII string enclosed in double quotes, or a series of octets specified in hexadecimal, seperated by colons. For example: .nf .sp 1 option dhcp-client-identifier "CLIENT-FOO"; or option dhcp-client-identifier 43:4c:49:45:54:2d:46:4f:4f; .fi .PP The documentation for the various options mentioned below is taken from the latest IETF draft document on DHCP options. Options which are not listed by name may be defined by the name option-\fInnn\fR, where \fInnn\fR is the decimal number of the option code. These options may be followed either by a string, enclosed in quotes, or by a series of octets, expressed as two-digit hexadecimal numbers seperated by colons. For example: .PP .nf option option-133 "my-option-133-text"; option option-129 1:54:c9:2b:47; .fi .PP Because dhcpd does not know the format of these undefined option codes, no checking is done to ensure the correctness of the entered data. .PP The standard options are: .PP .B option \fBall-subnets-local\fR \fIflag\fR\fB;\fR .RS 0.25i .PP This option specifies whether or not the client may assume that all subnets of the IP network to which the client is connected use the same MTU as the subnet of that network to which the client is directly connected. A value of true indicates that all subnets share the same MTU. A value of false means that the client should assume that some subnets of the directly connected network may have smaller MTUs. .RE .PP .B option \fBarp-cache-timeout\fR \fIuint32\fR\fB;\fR .RS 0.25i .PP This option specifies the timeout in seconds for ARP cache entries. .RE .PP .B option \fBbootfile-name\fR \fItext\fR\fB;\fR .RS 0.25i .PP This option is used to identify a bootstrap file. If supported by the client, it should have the same effect as the \fBfilename\fR declaration. BOOTP clients are unlikely to support this option. Some DHCP clients will support it, and others actually require it. .RE .PP .B option \fBboot-size\fR \fIuint16\fR\fB;\fR .RS 0.25i .PP This option specifies the length in 512-octet blocks of the default boot image for the client. .RE .PP .B option \fBbroadcast-address\fR \fIip-address\fR\fB;\fR .RS 0.25i .PP This option specifies the broadcast address in use on the client's subnet. Legal values for broadcast addresses are specified in section 3.2.1.3 of STD 3 (RFC1122). .RE .PP .B option \fBcookie-servers\fR \fIip-address\fR [\fB,\fR \fIip-address\fR... ]\fB;\fR .RS 0.25i .PP The cookie server option specifies a list of RFC 865 cookie servers available to the client. Servers should be listed in order of preference. .RE .PP .B option \fBdefault-ip-ttl\fR \fIuint8;\fR .RS 0.25i .PP This option specifies the default time-to-live that the client should use on outgoing datagrams. .RE .PP .B option \fBdefault-tcp-ttl\fR \fIuint8\fR\fB;\fR .RS 0.25i .PP This option specifies the default TTL that the client should use when sending TCP segments. The minimum value is 1. .RE .PP .B option \fBdhcp-client-identifier\fR \fIstring\fR\fB;\fR .RS 0.25i .PP This option can be used to specify the a DHCP client identifier in a host declaration, so that dhcpd can find the host record by matching against the client identifier. .RE .PP .B option \fBdhcp-max-message-size\fR \fIuint16\fR\fB;\fR .RS 0.25i .PP This option, when sent by the client, specifies the maximum size of any response that the server sends to the client. When specified on the server, if the client did not send a dhcp-max-message-size option, the size specified on the server is used. This works for BOOTP as well as DHCP responses. .RE .PP .B option \fBdhcp-parameter-request-list\fR \fIuint16\fR\fB;\fR .RS 0.25i .PP This option, when sent by the client, specifies which options the client wishes the server to return. Normally, in the ISC DHCP client, this is done using the \fIrequest\fR statement. If this option is not specified by the client, the DHCP server will normally return every option that is valid in scope and that fits into the reply. When this option is specified on the server, the server returns the specified options. This can be used to force a client to take options that it hasn't requested, and it can also be used to tailor the response of the DHCP server for clients that may need a more limited set of options than those the server would normally return. .RE .PP .B option \fBdomain-name\fR \fItext\fR\fB;\fR .RS 0.25i .PP This option specifies the domain name that client should use when resolving hostnames via the Domain Name System. .RE .PP .B option \fBdomain-name-servers\fR \fIip-address\fR [\fB,\fR \fIip-address\fR... ]\fB;\fR .RS 0.25i .PP The domain-name-servers option specifies a list of Domain Name System (STD 13, RFC 1035) name servers available to the client. Servers should be listed in order of preference. .RE .PP .B option \fBextensions-path-name\fR \fItext\fR\fB;\fR .RS 0.25i .PP This option specifies the name of a file containing additional options to be interpreted according to the DHCP option format as specified in RFC2132. .RE .PP .B option \fBfinger-server\fR \fIip-address\fR [\fB,\fR \fIip-address\fR... ]\fB;\fR .RS 0.25i .PP The Finger server option specifies a list of Finger available to the client. Servers should be listed in order of preference. .RE .PP .B option \fBfont-servers\fR \fIip-address\fR [\fB,\fR \fIip-address\fR... ]\fB;\fR .RS 0.25i .PP This option specifies a list of X Window System Font servers available to the client. Servers should be listed in order of preference. .RE .PP .B option \fBhost-name\fR \fIstring\fR\fB;\fR .RS 0.25i .PP This option specifies the name of the client. The name may or may not be qualified with the local domain name (it is preferable to use the domain-name option to specify the domain name). See RFC 1035 for character set restrictions. .RE .PP .B option \fBieee802-3-encapsulation\fR \fIflag\fR\fB;\fR .RS 0.25i .PP This option specifies whether or not the client should use Ethernet Version 2 (RFC 894) or IEEE 802.3 (RFC 1042) encapsulation if the interface is an Ethernet. A value of false indicates that the client should use RFC 894 encapsulation. A value of true means that the client should use RFC 1042 encapsulation. .RE .PP .B option \fBien116-name-servers\fR \fIip-address\fR [\fB,\fR \fIip-address\fR... ]; .RS 0.25i .PP The ien116-name-servers option specifies a list of IEN 116 name servers available to the client. Servers should be listed in order of preference. .RE .PP .B option \fBimpress-servers\fR \fIip-address\fR [\fB,\fR \fIip-address\fR... ]\fB;\fR .RS 0.25i .PP The impress-server option specifies a list of Imagen Impress servers available to the client. Servers should be listed in order of preference. .RE .PP .B option \fBinterface-mtu\fR \fIuint16\fR\fB;\fR .RS 0.25i .PP This option specifies the MTU to use on this interface. The minimum legal value for the MTU is 68. .RE .PP .B option \fBip-forwarding\fR \fIflag\fR\fB;\fR .RS 0.25i .PP This option specifies whether the client should configure its IP layer for packet forwarding. A value of false means disable IP forwarding, and a value of true means enable IP forwarding. .RE .PP .B option \fBirc-server\fR \fIip-address\fR [\fB,\fR \fIip-address\fR... ]\fB;\fR .RS 0.25i .PP The IRC server option specifies a list of IRC available to the client. Servers should be listed in order of preference. .RE .PP .B option \fBlog-servers\fR \fIip-address\fR [\fB,\fR \fIip-address\fR... ]\fB;\fR .RS 0.25i .PP The log-server option specifies a list of MIT-LCS UDP log servers available to the client. Servers should be listed in order of preference. .RE .PP .B option \fBlpr-servers\fR \fIip-address \fR [\fB,\fR \fIip-address\fR... ]\fB;\fR .RS 0.25i .PP The LPR server option specifies a list of RFC 1179 line printer servers available to the client. Servers should be listed in order of preference. .RE .PP .B option \fBmask-supplier\fR \fIflag\fR\fB;\fR .RS 0.25i .PP This option specifies whether or not the client should respond to subnet mask requests using ICMP. A value of false indicates that the client should not respond. A value of true means that the client should respond. .RE .PP .B option \fBmax-dgram-reassembly\fR \fIuint16\fR\fB;\fR .RS 0.25i .PP This option specifies the maximum size datagram that the client should be prepared to reassemble. The minimum value legal value is 576. .RE .PP .B option \fBmerit-dump\fR \fItext\fR\fB;\fR .RS 0.25i .PP This option specifies the path-name of a file to which the client's core image should be dumped in the event the client crashes. The path is formatted as a character string consisting of characters from the NVT ASCII character set. .RE .PP .B option \fBmobile-ip-home-agent\fR \fIip-address\fR [\fB,\fR \fIip-address\fR... ]\fB;\fR .RS 0.25i .PP This option specifies a list of IP addresses indicating mobile IP home agents available to the client. Agents should be listed in order of preference, although normally there will be only one such agent. .RE .PP .B option \fBnds-context\fR \fIstring\fR\fB;\fR .RS 0.25i .PP The nds-context option specifies the name of the initial Netware Directory Service for an NDS client. .RE .PP .B option \fBnds-servers\fR \fIip-address\fR [\fB,\fR \fIip-address\fR... ]\fB;\fR .RS 0.25i .PP The nds-servers option specifies a list of IP addresses of NDS servers. .RE .PP .B option \fBnds-tree-name\fR \fIstring\fR\fB;\fR .RS 0.25i .PP The nds-context option specifies NDS tree name that the NDS client should use. .RE .PP .B option \fBnetbios-dd-server\fR \fIip-address\fR [\fB,\fR \fIip-address\fR... ]\fB;\fR .RS 0.25i .PP The NetBIOS datagram distribution server (NBDD) option specifies a list of RFC 1001/1002 NBDD servers listed in order of preference. .RE .PP .B option \fBnetbios-name-servers\fR \fIip-address\fR [\fB,\fR \fIip-address\fR...]\fB;\fR .RS 0.25i .PP The NetBIOS name server (NBNS) option specifies a list of RFC 1001/1002 NBNS name servers listed in order of preference. NetBIOS Name Service is currently more commonly referred to as WINS. WINS servers can be specified using the netbios-name-servers option. .RE .PP .B option \fBnetbios-node-type\fR \fIuint8\fR\fB;\fR .RS 0.25i .PP The NetBIOS node type option allows NetBIOS over TCP/IP clients which are configurable to be configured as described in RFC 1001/1002. The value is specified as a single octet which identifies the client type. .PP Possible node types are: .PP .TP 5 .I 1 B-node: Broadcast - no WINS .TP .I 2 P-node: Peer - WINS only. .TP .I 4 M-node: Mixed - broadcast, then WINS .TP .I 8 H-node: Hybrid - WINS, then broadcast .RE .PP .B option \fBnetbios-scope\fR \fIstring\fR\fB;\fR .RS 0.25i .PP The NetBIOS scope option specifies the NetBIOS over TCP/IP scope parameter for the client as specified in RFC 1001/1002. See RFC1001, RFC1002, and RFC1035 for character-set restrictions. .RE .PP .B option \fBnwip-domain\fR \fIstring\fR\fB;\fR .RS 0.25i .PP The name of the NetWare/IP domain that a NetWare/IP client should use. .RE .PP .B option \fBnwip-suboptions\fR \fIstring\fR\fB;\fR .RS 0.25i .PP A sequence of suboptions for NetWare/IP clients - see RFC2242 for details. Normally this option is set by specifying specific NetWare/IP suboptions - see the NETWARE/IP SUBOPTIONS section for more information. .RE .PP .B option \fBnis-domain\fR \fItext\fR\fB;\fR .RS 0.25i .PP This option specifies the name of the client's NIS (Sun Network Information Services) domain. The domain is formatted as a character string consisting of characters from the NVT ASCII character set. .RE .PP .B option \fBnis-servers\fR \fIip-address\fR [\fB,\fR \fIip-address\fR... ]\fB;\fR .RS 0.25i .PP This option specifies a list of IP addresses indicating NIS servers available to the client. Servers should be listed in order of preference. .RE .PP .B option \fBnisplus-domain\fR \fItext\fR\fB;\fR .RS 0.25i .PP This option specifies the name of the client's NIS+ domain. The domain is formatted as a character string consisting of characters from the NVT ASCII character set. .RE .PP .B option \fBnisplus-servers\fR \fIip-address\fR [\fB,\fR \fIip-address\fR... ]\fB;\fR .RS 0.25i .PP This option specifies a list of IP addresses indicating NIS+ servers available to the client. Servers should be listed in order of preference. .RE .PP .B option \fBnntp-server\fR \fIip-address\fR [\fB,\fR \fIip-address\fR... ]\fB;\fR .RS 0.25i .PP The NNTP server option specifies a list of NNTP available to the client. Servers should be listed in order of preference. .RE .PP .B option \fBnon-local-source-routing\fR \fIflag\fR\fB;\fR .RS 0.25i .PP This option specifies whether the client should configure its IP layer to allow forwarding of datagrams with non-local source routes (see Section 3.3.5 of [4] for a discussion of this topic). A value of 0 means disallow forwarding of such datagrams, and a value of true means allow forwarding. .RE .PP .B option \fBntp-servers\fR \fIip-address\fR [\fB,\fR \fIip-address\fR... ]\fB;\fR .RS 0.25i .PP This option specifies a list of IP addresses indicating NTP (RFC 1035) servers available to the client. Servers should be listed in order of preference. .RE .PP .B option \fBpath-mtu-aging-timeout\fR \fIuint32\fR\fB;\fR .RS 0.25i .PP This option specifies the timeout (in seconds) to use when aging Path MTU values discovered by the mechanism defined in RFC 1191. .RE .PP .B option \fBpath-mtu-plateau-table\fR \fIuint16\fR [\fB,\fR \fIuint16\fR... ]\fB;\fR .RS 0.25i .PP This option specifies a table of MTU sizes to use when performing Path MTU Discovery as defined in RFC 1191. The table is formatted as a list of 16-bit unsigned integers, ordered from smallest to largest. The minimum MTU value cannot be smaller than 68. .RE .PP .B option \fBperform-mask-discovery\fR \fIflag\fR\fB;\fR .RS 0.25i .PP This option specifies whether or not the client should perform subnet mask discovery using ICMP. A value of false indicates that the client should not perform mask discovery. A value of true means that the client should perform mask discovery. .RE .PP .nf .B option \fBpolicy-filter\fR \fIip-address ip-address\fR [\fB,\fR \fIip-address ip-address\fR...]\fB;\fR .RE .fi .RS 0.25i .PP This option specifies policy filters for non-local source routing. The filters consist of a list of IP addresses and masks which specify destination/mask pairs with which to filter incoming source routes. .PP Any source routed datagram whose next-hop address does not match one of the filters should be discarded by the client. .PP See STD 3 (RFC1122) for further information. .RE .PP .B option \fBpop-server\fR \fIip-address\fR [\fB,\fR \fIip-address\fR... ]\fB;\fR .RS 0.25i .PP The POP3 server option specifies a list of POP3 available to the client. Servers should be listed in order of preference. .RE .PP .nf .B option \fBresource-location-servers\fR \fIip-address\fR [\fB, \fR\fIip-address\fR...]\fB;\fR .fi .RS 0.25i .PP This option specifies a list of RFC 887 Resource Location servers available to the client. Servers should be listed in order of preference. .RE .PP .B option \fBroot-path\fR \fItext\fB;\fR\fR .RS 0.25i .PP This option specifies the path-name that contains the client's root disk. The path is formatted as a character string consisting of characters from the NVT ASCII character set. .RE .PP .B option \fBrouter-discovery\fR \fIflag\fR\fB;\fR .RS 0.25i .PP This option specifies whether or not the client should solicit routers using the Router Discovery mechanism defined in RFC 1256. A value of false indicates that the client should not perform router discovery. A value of true means that the client should perform router discovery. .RE .PP .B option \fBrouter-solicitation-address\fR \fIip-address\fR\fB;\fR .RS 0.25i .PP This option specifies the address to which the client should transmit router solicitation requests. .RE .PP .B option routers \fIip-address\fR [\fB,\fR \fIip-address\fR... ]\fB;\fR .RS 0.25i .PP The routers option specifies a list of IP addresses for routers on the client's subnet. Routers should be listed in order of preference. .RE .PP .B option \fBsmtp-server\fR \fIip-address\fR [\fB,\fR \fIip-address\fR... ]\fB;\fR .RS 0.25i .PP The SMTP server option specifies a list of SMTP servers available to the client. Servers should be listed in order of preference. .RE .PP .nf .B option \fBstatic-routes\fR \fIip-address ip-address\fR [\fB,\fR \fIip-address ip-address\fR...]\fB;\fR .fi .RS 0.25i .PP This option specifies a list of static routes that the client should install in its routing cache. If multiple routes to the same destination are specified, they are listed in descending order of priority. .PP The routes consist of a list of IP address pairs. The first address is the destination address, and the second address is the router for the destination. .PP The default route (0.0.0.0) is an illegal destination for a static route. To specify the default route, use the .B routers option. Also, please note that this option is not intended for classless IP routing - it does not include a subnet mask. Since classless IP routing is now the most widely deployed routing standard, this option is virtually useless, and is not implemented by any of the popular DHCP clients, for example the Microsoft DHCP client. .RE .PP .nf .B option \fBstreettalk-directory-assistance-server\fR \fIip-address\fR [\fB,\fR \fIip-address\fR...]\fB;\fR .fi .RS 0.25i .PP The StreetTalk Directory Assistance (STDA) server option specifies a list of STDA servers available to the client. Servers should be listed in order of preference. .RE .PP .B option \fBstreettalk-server\fR \fIip-address\fR [\fB,\fR \fIip-address\fR... ]\fB;\fR .RS 0.25i .PP The StreetTalk server option specifies a list of StreetTalk servers available to the client. Servers should be listed in order of preference. .RE .PP .B option subnet-mask \fIip-address\fR\fB;\fR .RS 0.25i .PP The subnet mask option specifies the client's subnet mask as per RFC 950. If no subnet mask option is provided anywhere in scope, as a last resort dhcpd will use the subnet mask from the subnet declaration for the network on which an address is being assigned. However, .I any subnet-mask option declaration that is in scope for the address being assigned will override the subnet mask specified in the subnet declaration. .RE .PP .B option \fBswap-server\fR \fIip-address\fR\fB;\fR .RS 0.25i .PP This specifies the IP address of the client's swap server. .RE .PP .B option \fBtcp-keepalive-garbage\fR \fIflag\fR\fB;\fR .RS 0.25i .PP This option specifies the whether or not the client should send TCP keepalive messages with a octet of garbage for compatibility with older implementations. A value of false indicates that a garbage octet should not be sent. A value of true indicates that a garbage octet should be sent. .RE .PP .B option \fBtcp-keepalive-interval\fR \fIuint32\fR\fB;\fR .RS 0.25i .PP This option specifies the interval (in seconds) that the client TCP should wait before sending a keepalive message on a TCP connection. The time is specified as a 32-bit unsigned integer. A value of zero indicates that the client should not generate keepalive messages on connections unless specifically requested by an application. .RE .PP .B option \fBtftp-server-name\fR \fItext\fR\fB;\fR .RS 0.25i .PP This option is used to identify a TFTP server and, if supported by the client, should have the same effect as the \fBserver-name\fR declaration. BOOTP clients are unlikely to support this option. Some DHCP clients will support it, and others actually require it. .RE .PP .B option time-offset \fIint32\fR\fB;\fR .RS 0.25i .PP The time-offset option specifies the offset of the client's subnet in seconds from Coordinated Universal Time (UTC). .RE .PP .B option time-servers \fIip-address\fR [, \fIip-address\fR... ]\fB;\fR .RS 0.25i .PP The time-server option specifies a list of RFC 868 time servers available to the client. Servers should be listed in order of preference. .RE .PP .B option \fBtrailer-encapsulation\fR \fIflag\fR\fB;\fR .RS 0.25i .PP This option specifies whether or not the client should negotiate the use of trailers (RFC 893 [14]) when using the ARP protocol. A value of 0 indicates that the client should not attempt to use trailers. A value of true means that the client should attempt to use trailers. .RE .PP .B option \fBuap-servers\fR \fItext\fR\fB;\fR .RS 0.25i .PP This option specifies a list of URLs, each pointing to a user authentication service that is capable of processing authentication requests encapsulated in the User Authentication Protocol (UAP). UAP servers can accept either HTTP 1.1 or SSLv3 connections. If the list includes a URL that does not contain a port component, the normal default port is assumed (i.e., port 80 for http and port 443 for https). If the list includes a URL that does not contain a path component, the path /uap is assumed. If more than one URL is specified in this list, the URLs are seperated by spaces. .RE .PP .B option \fBvendor-class-identifier\fR \fIstring\fR\fB;\fR .RS 0.25i .PP This option is used by some DHCP clients to identify the vendor type and possibly the configuration of a DHCP client. The information is a string of bytes whose contents are specific to the vendor and are not specified in a standard. To see what vendor class identifier a clients are sending, you can write the following in your DHCP server configuration file: .nf .PP set vendor-class option vendor-class-identifier; .fi .PP This will result in all entries in the DHCP server lease database file for clients that sent vendor-class-identifier options having a set statement that looks something like this: .nf .PP set vendor-class "SUNW.Ultra-5_10"; .fi .PP The vendor-class-identifier option is normally used by the DHCP server to determine the options that are returned in the .B vendor-encapsulated-options option. Please see the VENDOR ENCAPSULATED OPTIONS section of the dhcpd.conf manual page for further information. .RE .PP .B option \fBvendor-encapsulated-options\fR \fIstring\fR\fB;\fR .RS 0.25i .PP The \fBvendor-encapsulated-options\fR option can contain either a single vendor-specific value or one or more vendor-specific suboptions. This option is not normally specified in the DHCP server configuration file - instead, a vendor class is defined for each vendor, vendor class suboptions are defined, values for those suboptions are defined, and the DHCP server makes up a response on that basis. .PP Some default behaviours for well-known DHCP client vendors (currently, the Microsoft Windows 2000 DHCP client) are configured automatically, but otherwise this must be configured manually - see the VENDOR ENCAPSULATED OPTIONS section of the \fIdhcpd.conf\fI manual page for details. .RE .PP .B option \fBx-display-manager\fR \fIip-address\fR [\fB,\fR \fIip-address\fR... ]\fB;\fR .RS 0.25i .PP This option specifies a list of systems that are running the X Window System Display Manager and are available to the client. Addresses should be listed in order of preference. .RE .PP .B option \fBwww-server\fR \fIip-address\fR [\fB,\fR \fIip-address\fR... ]\fB;\fR .RS 0.25i .PP The WWW server option specifies a list of WWW available to the client. Servers should be listed in order of preference. .RE .SH RELAY AGENT INFORMATION OPTION An IETF draft, draft-ietf-dhc-agent-options-03.txt, defines a series of encapsulated options that a relay agent can add to a DHCP packet when relaying it to the DHCP server. The server can then make address allocation decisions (or whatever other decisions it wants) based on these options. The server also returns these options in any replies it sends through the relay agent, so that the relay agent can use the information in these options for delivery or accounting purposes. .PP The current draft defines two options. To reference these options in the dhcp server, specify the option space name, "agent", followed by a period, followed by the option name. It isn't useful to specify these options to be sent, nor is it useful to reference them at all in the client. .PP .B option \fBagent.circuit-id\fR \fIstring\fR\fB;\fR .RS 0.25i .PP The circuit-id suboption encodes an agent-local identifier of the circuit from which a DHCP client-to-server packet was received. It is intended for use by agents in relaying DHCP responses back to the proper circuit. The format of this option is currently defined to be vendor-dependent, and will probably remain that way, although the current draft allows for for the possibility of standardizing the format in the future. .RE .PP .B option \fBagent.remote-id\fR \fIstring\fR\fB;\fR .RS 0.25i .PP The remote-id suboption encodes information about the remote host end of a circuit. Examples of what it might contain include caller ID information, username information, remote ATM address, cable modem ID, and similar things. In principal, the meaning is not well-specified, and it should generally be assumed to be an opaque object that is administratively guaranteed to be unique to a particular remote end of a circuit. .RE .SH THE NETWARE/IP SUBOPTIONS RFC2242 defines a set of encapsulated options for Novell NetWare/IP clients. To use these options in the dhcp server, specify the option space name, "nwip", followed by a period, followed by the option name. The following options can be specified: .PP .B option \fBnwip.nsq-broadcast\fR \fIflag\fR\fB;\fR .RS 0.25i .PP If true, the client should use the NetWare Nearest Server Query to locate a NetWare/IP server. The behaviour of the Novell client if this suboption is false, or is not present, is not specified. .PP .RE .B option \fBnwip.preferred-dss\fR \fIip-address\fR [\fB,\fR \fIip-address\fR... ]\fR\fB;\fR .RS 0.25i .PP This suboption specifies a list of up to five IP addresses, each of which should be the IP address of a NetWare Domain SAP/RIP server (DSS). .RE .PP .B option \fBnwip.nearest-nwip-server\fR \fI\fIip-address\fR [\fB,\fR \fIip-address\fR...]\fR\fB;\fR .RS 0.25i .PP This suboption specifies a list of up to five IP addresses, each of which should be the IP address of a Nearest NetWare IP server. .RE .PP .B option \fBnwip.autoretries\fR \fIuint8\fR\fB;\fR .RS 0.25i .PP Specifies the number of times that a NetWare/IP client should attempt to communicate with a given DSS server at startup. .RE .PP .B option \fBnwip.autoretry-secs\fR \fIuint8\fR\fB;\fR .RS 0.25i .PP Specifies the number of seconds that a Netware/IP client should wait between retries when attempting to establish communications with a DSS server at startup. .RE .PP .B option \fBnwip.nwip-1-1\fR \fIuint8\fR\fB;\fR .RS 0.25i .PP If true, the NetWare/IP client should support NetWare/IP version 1.1 compatibility. This is only needed if the client will be contacting Netware/IP version 1.1 servers. .RE .PP .B option \fBnwip.primary-dss\fR \fIip-address\fR\fB;\fR .RS 0.25i .PP Specifies the IP address of the Primary Domain SAP/RIP Service server (DSS) for this NetWare/IP domain. The NetWare/IP administration utility uses this value as Primary DSS server when configuring a secondary DSS server. .RE .SH DEFINING NEW OPTIONS The Internet Software Consortium DHCP client and server provide the capability to define new options. Each DHCP option has a name, a code, and a structure. The name is used by you to refer to the option. The code is a number, used by the DHCP server and client to refer to an option. The structure describes what the contents of an option looks like. .PP To define a new option, you need to choose a name for it that is not in use for some other option - for example, you can't use "host-name" because the DHCP protocol already defines a host-name option, which is documented earlier in this manual page. If an option name doesn't appear in this manual page, you can use it, but it's probably a good idea to put some kind of unique string at the beginning so you can be sure that future options don't take your name. For example, you might define an option, "local-host-name", feeling some confidence that no official DHCP option name will ever start with "local". .PP Once you have chosen a name, you must choose a code. For site-local options, all codes between 128 and 254 are reserved for DHCP options, so you can pick any one of these. In practice, some vendors have interpreted the protocol rather loosely and have used option code values greater than 128 themselves. There's no real way to avoid this problem, but it's not likely to cause too much trouble in practice. .PP The structure of an option is simply the format in which the option data appears. The ISC DHCP server currently supports a few simple types, like integers, booleans, strings and IP addresses, and it also supports the ability to define arrays of single types or arrays of fixed sequences of types. .PP New options are declared as follows: .PP .B option .I new-name .B code .I new-code .B = .I definition .B ; .PP The values of .I new-name and .I new-code should be the name you have chosen for the new option and the code you have chosen. The .I definition should be the definition of the structure of the option. .PP The following simple option type definitions are supported: .PP .B BOOLEAN .PP .B option .I new-name .B code .I new-code .B = .B boolean .B ; .PP An option of type boolean is a flag with a value of either on or off (or true or false). So an example use of the boolean type would be: .nf option use-zephyr code 180 = boolean; option use-zephyr on; .fi .B INTEGER .PP .B option .I new-name .B code .I new-code .B = .I sign .B integer .I width .B ; .PP The \fIsign\fR token should either be blank, \fIunsigned\fR or \fIsigned\fR. The width can be either 8, 16 or 32, and refers to the number of bits in the integer. So for example, the following two lines show a definition of the sql-connection-max option and its use: .nf option sql-connection-max code 192 = unsigned integer 16; option sql-connection-max 1536; .fi .B IP-ADDRESS .PP .B option .I new-name .B code .I new-code .B = .B ip-address .B ; .PP An option whose structure is an IP address can be expressed either as a domain name or as a dotted quad. So the following is an example use of the ip-address type: .nf option sql-server-address code 193 = ip-address; option sql-server-address sql.example.com; .fi .PP .B TEXT .PP .B option .I new-name .B code .I new-code .B = .B text .B ; .PP An option whose type is text will encode an ASCII text string. For example: .nf option sql-default-connection-name code 194 = text; option sql-default-connection-name "PRODZA"; .fi .PP .B DATA STRING .PP .B option .I new-name .B code .I new-code .B = .B string .B ; .PP An option whose type is a data string is essentially just a collection of bytes, and can be specified either as quoted text, like the text type, or as a list of hexadecimal contents seperated by colons whose values must be between 0 and FF. For example: .nf option sql-identification-token code 195 = string; option sql-identification-token 17:23:19:a6:42:ea:99:7c:22; .fi .PP .B ARRAYS .PP Options can contain arrays of any of the above types except for the text and data string types, which aren't currently supported in arrays. An example of an array definition is as follows: .nf option kerberos-servers code 200 = array of ip-address; option kerberos-servers 10.20.10.1, 10.20.11.1; .fi .B RECORDS .PP Options can also contain data structures consisting of a sequence of data types, which is sometimes called a record type. For example: .nf option contrived-001 code 201 = { boolean, integer 32, text }; option contrived-001 on 1772 "contrivance"; .fi It's also possible to have options that are arrays of records, for example: .nf option new-static-routes code 201 = array of { ip-address, ip-address, ip-address, integer 8 }; option static-routes 10.0.0.0 255.255.255.0 net-0-rtr.example.com 1, 10.0.1.0 255.255.255.0 net-1-rtr.example.com 1, 10.2.0.0 255.255.224.0 net-2-0-rtr.example.com 3; .fi .SH VENDOR ENCAPSULATED OPTIONS The DHCP protocol defines the \fB vendor-encapsulated-options\fR option, which allows vendors to define their own options that will be sent encapsulated in a standard DHCP option. The format of the .B vendor-encapsulated-options option is either a series of bytes whose format is not specified, or a sequence of options, each of which consists of a single-byte vendor-specific option code, followed by a single-byte length, followed by as many bytes of data as are specified in the length (the length does not include itself or the option code). .PP The value of this option can be set in one of two ways. The first way is to simply specify the data directly, using a text string or a colon-seperated list of hexadecimal values. For example: .PP .nf option vendor-encapsulated-options 2:4:AC:11:41:1: 3:12:73:75:6e:64:68:63:70:2d:73:65:72:76:65:72:31:37:2d:31: 4:12:2f:65:78:70:6f:72:74:2f:72:6f:6f:74:2f:69:38:36:70:63; .fi .PP The second way of setting the value of this option is to have the DHCP server generate a vendor-specific option buffer. To do this, you must do four things: define an option space, define some options in that option space, provide values for them, and specify that that option space should be used to generate the .B vendor-encapsulated-options option. .PP To define a new option space in which vendor options can be stored, use the \fRoption space\fP statement: .PP .B option .B space .I name .B ; .PP The name can then be used in option definitions, as described earlier in this document. For example: .nf option space SUNW; option SUNW.server-address code 2 = ip-address; option SUNW.server-name code 3 = text; option SUNW.root-path code 4 = text; .fi Once you have defined an option space and the format of some options, you can set up scopes that define values for those options, and you can say when to use them. For example, suppose you want to handle two different classes of clients. Using the option space definition shown in the previous example, you can send different option values to different clients based on the vendor-class-identifier option that the clients send, as follows: .PP .nf class "vendor-classes" { match option vendor-class-identifier; } option SUNW.server-address 172.17.65.1; option SUNW.server-name "sundhcp-server17-1"; subclass "vendor-classes" "SUNW.Ultra-5_10" { vendor-option-space SUNW; option SUNW.root-path "/export/root/sparc"; } subclass "vendor-classes" "SUNW.i86pc" { vendor-option-space SUNW; option SUNW.root-path "/export/root/i86pc"; } .fi .PP As you can see in the preceding example, regular scoping rules apply, so you can define values that are global in the global scope, and only define values that are specific to a particular class in the local scope. The \fBvendor-option-space\fR declaration tells the DHCP server to use options in the SUNW option space to construct the .B vendor-encapsulated-options option. .SH SEE ALSO dhcpd.conf(5), dhcpd.leases(5), dhclient.conf(5), dhcp-eval(5), dhcpd(8), dhclient(8), RFC2132, RFC2131, draft-ietf-dhc-agent-options-??.txt. .SH AUTHOR The Internet Software Consortium DHCP Distribution was written by Ted Lemon under a contract with Vixie Labs. Funding for this project was provided through the Internet Software Consortium. Information about the Internet Software Consortium can be found at .B http://www.isc.org/isc.