ISC DHCPv4 Option Configuration

DHCP option values can be defined on a global or scoped basis to influence the configuration parameters of devices initializing via DHCP. Within the relevant scope the option is declared using the following general syntax which is equivalent to that for DHCP for IPv4:

option option-name option-value;


  • option is the keyword indicating that an option is specified on this line.
  • option-name is the name of the option according to the server
  • option-value is the actual value of the option to provide to the client.

The following table summarizes the DHCP options currently supported along with the corresponding ISC DHCP option-name and option-value data type. The Tag and Name columns in the table provide a cross reference to the Internet standard option defintions.

Tag Name option-name option-value type
1Subnet Masksubnet-maskIP address formatted mask
2Time Offsettime-offsetinteger - seconds offset from UTC
3Router (Default Gateway)routersIP address(es) in preferred order
4Time Servertime-serversIP address(es) in preferred order
5Name Serverien116-name-serversIP address(es) of IEN 116 name server(s)
in preferred order
6Domain Serverdomain-name-serversIP address(es) in preferred order
7Log Serverlog-serversIP address(es) in preferred order
8Quotes Servercookie-serversIP address(es) in preferred order
9LPR Serverlpr-serversIP address(es) in preferred order
10Impress Serverimpress-serversIP address(es) in preferred order
11RLP Serverresource-location-serversIP address(es) in preferred order
12Hostnamehost-nametext string
13Boot File Sizeboot-sizeinteger
14Merit Dump Filemerit-dumptext (filename)
15Domain Namedomain-nametext - client's domain name of the client
16Swap Serverswap-serverIP address
17Root Pathroot-pathtext (directory path)
18Extension Fileextensions-pathtext (filename)
19Forward On/Offip-forwarding* true = enable IP forwarding
* false = disable
20Source Routingnon-local-source-routing* true = enable forwarding of datagrams with non-local source routing
* false = disable
21Policy Filterpolicy-filterIP address pair(s) consisting of destination and corresponding mask for filtering of source-routed datagrams separated by a space; multiple pairs are comma separated.
22Max Datagram Size
for Reassembly
max-dgram-reassemblyinteger (minimum = 576)
23Default IP TTLdefault-ip-ttlinteger
24MTU Timeoutpath-mtu-aging-timeoutinteger (seconds)
25MTU Plateaupath-mtu-plateau-tableinteger(s) - (68 is the minimum value of each)
26MTU Interfaceinterface-mtuMTU for a given interface (68 is the minimum value)
27MTU Subnetall-subnets-localtrue or false
28Broadcast Addressbroadcast-addressIP address
29Mask Discoveryperform-mask-discovery* true = client should perform subnet mask discovery using ICMP
* false = client should not do so
30Mask Suppliermask-supplier*true = client should respond to ICMP subnet mask requests
* false = client shouldn't respond
31Router Discoveryrouter-discovery* true = client should perform router discovery per RFC 1256
*false = client should not perform router discovery
32Router Requestrouter-solicitation-addressIP address
33Static Routestatic-routesIP address pair(s): destination address and corresponding router separated by space; multiple pairs comma separated; use routers option (3) to specify a default route
34Trailerstrailer-encapsulation* true = use trailers (RFC 893) when using ARP
* false = do not use trailers
35ARP Timeoutarp-cache-timeoutinteger (seconds)
36Ethernetieee802-3-encapsulation* true = 802.3 encapsulation
* false = Ethernet2 (RFC 894)
37Default TCP TTLdefault-tcp-ttlinteger (seconds)
38Keepalive Timetcp-keepalive-intervalinteger (seconds)
39Keepalive Datatcp-keepalive-garbage* true = send a garbage octet with keepalive messages for backward TCP compatibility
* false = do not send garbage octet
40NIS Domainnis-domaintext
41NIS Serversnis-serversIP address(es) in preferred order
42NTP Serversntp-serversIP address(es) in preferred order
43Vendor Specificvendor-encapsulated-optionsstring of vendor-specific information
44NETBIOS Name Servernetbios-name-serversIP address(es) in preferred order
45NETBIOS Dist Servernetbios-dd-serverIP address(es) in preferred order
46NETBIOS Node Typenetbios-node-typeinteger encoding of node type:
 1 = B-node - broadcast no WINS
 2 = P-node - WINS only
 3 = M-node - broadcast then WINS
 4 = H-node - WINS then broadcast
47NETBIOS Scopenetbios-scopestring encoded in accordance with RFCs 1001-1002
48X Window Fontfont-serversIP address(es) in preferred order
49X Window Managerx-display-managerIP address(es) in preferred order
50Address Requestdhcp-requested-addressN/A - used by the client to request a particular
IP address
51Address Timedhcp-lease-timeN/A - used by client to request a lease time (this option is not configurable on the ISC DHCP server - config file parameters max-lease-time and default-lease-time are used)
52Overloaddhcp-option-overloadinteger indicating which DHCP header field(s) hold options:
 1 = “file” field
 2 = “sname” field
 3 = both “file” and “sname” fields
53DHCP Message Typedhcp-message-typeN/A used to identify message type
54DHCP Server Identifierdhcp-server-identifierN/A - server-identifier parameter in the
config file is used instead
55Parameter Listdhcp-parameter-request-listinteger(s) denoting options to provide to
the client
56DHCP Messagedhcp-messageN/A - used to populate an error message from the server with a DHCPNAK or from a client in a DHCPDECLINE message
57DHCP Max Msg Sizedhcp-max-message-sizeinteger - used as a default if not provided by the client
58Renewal Timedhcp-renewal-timeN/A - based on the lease time
59Rebinding Timedhcp-rebinding-timeN/A - based on the lease time
60Vendor Class Idvendor-class-identifierstring
61Client Iddhcp-client-identifiertext (string or hex digits) - be aware that some clients prepend a 0 to the ASCII text so you may have to encode "\\ 0foo" instead of just “foo”
62Netware/IP Domainnwip-domainstring
63Netware/IP Options - specify as single hex string or per suboptionnwip-suboptions
string of all options in hex
IP address(es)
IP address(es)
IP address
64NIS+ Domain Namenisplus-domaintext (domain name)
65NIS+ Server Addressnisplus-serversIP address(es) in preferred order
66Server Nametftp-server-nametext (server domain name)
67Bootfile Namebootfile-nametext (file name)
68Home Agent Addressesmobile-ip-home-agentIP address(es) in preferred order
69SMTP Serversmtp-serverIP address(es) in preferred order
70POP3 Serverpop-serverIP address(es) in preferred order
71NNTP Servernntp-serverIP address(es) in preferred order
72WWW Serverwww-serverIP address(es) in preferred order
73Finger Serverfinger-serverIP address(es) in preferred order
74IRC Serverirc-serverIP address(es) in preferred order
75StreetTalk Serverstreettalk-serverIP address(es) in preferred order
76StreetTalk Directory
Assistance (STDA) Server
IP address(es)
77User Classuser-classstring
78Service Location Protocol
(SLP) Directory Agent
slp-directory-agentTwo parameters (space separated):
* Boolean - true = use only addresses provided in this option; false = use provided options and others via SLP agent discovery
* IP address(es) of SLP directory agent(s)
79SLP Service Scopeslp-service-scopeTwo parameters (space separated):
* Boolean - true = use only service scope(s) provided in this option; false = use provided scope(s) and others statically configured
* text string(s) of service scope(es)
80Rapid CommitN/A - sent by client to request 2 packettransaction instead of the normal 4 packet transaction
81Client FQDNfqdn option spaceN/A - sent by client regarding DDNS update.
Please refer to the Client FQDN Option
for server parameters associated with this option
82Relay Agent Informationagent.circuit-id agent.remote-id agent.DOCSIS-device-class for setting values. Please refer to the Relay Agent Information Options page for more details.
83iSNSNot natively supportedN/A
85NDS Serversnds-serversIP address(es)
86NDS Tree Namends-tree-namestring
87NDS Contextnds-contextstring
88BCMCS Controller
Domain Name
bcms-controller-namesdomain list
89BCMCS Controller
IPv4 address option
bcms-controller-addressIP address list
90AuthenticationN/A - used to pass DHCP authentication information
time option
N/A - used as part of DHCP Lease Query
92Associated-ip optionN/A - used as part of DHCP Lease Query
93Client SystemN/A - used by PXE clients to convey the client hardware architecture to the server
94Client NDIN/A - used by PXE clients to convey the client's
network interface type to the server
95LDAPNot natively supported N/A
97UUID/GUIDN/A - used by PXE clients to convey the client's unique identifier to the server
98User Authentication
uap-serverstext (URL list)
99GEOCONF_ CIVICNot natively supportedN/A
112Netinfo Addressnetinfo-server-addressIP address(es) - not defined in any RFC but assigned by IANA
113Netinfo Tagnetinfo-server-tagtest string - - not defined in any RFC but assigned by IANA
114Default URLdefault-urltext (URL) - not defined in any RFC but assigned by IANA
116Auto-ConfigN/A - used by clients to request auto-configuration support from the server
117Name Service SearchNot natively supportedN/A
118Subnet Selection Optionsubnet-selectionN/A - client preferred subnet for address assignment
119Domain Searchdomain-searchOne or more domain names each enclosed in quotes and separated by commas
120SIP Servers DHCP OptionNot natively supportedN/A
121Classless Static Route
Not natively supportedN/A
122CCCNot natively supportedN/A
123GeoConf OptionNot natively supportedN/A
124Vendor Identified
Vendor Class
N/A - sent by client to convey its vendor-identified vendor class
125Vendor Identified Vendor-
Specific Information