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This is the documentation for the 19.12 version. Looking for the documentation of the latest version? Have a look here.

DHCP Options

DHCP Options provide information to clients beyond the basic address assignment. These options give clients other aspects of the network configuration, tell clients how they should behave on the network, and give them information about services available on the network. Common examples are a default gateway, DNS Servers, Network Time Protocol servers, network booting behavior, and dozens of other possibilities.

See also

For a list of Standard IPv4 DHCP options, see Standard IPv4 DHCP Options. This list also includes the type of data expected and whether or not they take multiple values.

The general form of an option is:

tnsr(config-kea-dhcp4)# option <name>
tnsr(config-kea-dhcp4-opt)# data <comma-separated values>
tnsr(config-kea-dhcp4-opt)# exit

This example defines a global domain name for all clients in all subnets:

tnsr(config-kea-dhcp4)# option domain-name
tnsr(config-kea-dhcp4-opt)# data example.com
tnsr(config-kea-dhcp4-opt)# exit

This example defines a default gateway for a specific subnet:

tnsr(config-kea-subnet4)# option routers
tnsr(config-kea-subnet4-opt)# data 10.2.0.1
tnsr(config-kea-subnet4-opt)# exit

To see a list of option names, enter:

tnsr(config-kea-dhcp4)# option ?

When defining options the data can take different forms. The DHCP daemon uses comma-separated value (CSV) format by default and it will automatically convert the text representation of a value to the expected data in the daemon.

Inside the option configuration mode, the following choices are available:

always-send <boolean>:

Controls whether the DHCP server will always send this option in a response, or only when requested by a client. The default behavior varies by option and is documented in Standard IPv4 DHCP Options

csv-format <boolean>:

Toggles between either CSV formatted data or raw binary data. This defaults to true unless an option does not have a default definition. In nearly all cases this option should be left at the default.

data <data>:

Arbitrary option data. Do not enclose in quotes. To see option data types and expected formats, see Standard IPv4 DHCP Options

space <name>:

Option space in which this entry exists, defaults to dhcp4.

Standard IPv4 DHCP Options

This list contains information about the standard IPv4 DHCP options, sourced from the Kea Administrator Manual section on DHCP Options.

For a list of the Types and their possible values, see DHCP Option Types.

Name	Code	Type	Array	Always Return
time-offset	2	int32	false	false
routers	3	ipv4-address	true	true
time-servers	4	ipv4-address	true	false
name-servers	5	ipv4-address	true	false
domain-name-servers	6	ipv4-address	true	true
log-servers	7	ipv4-address	true	false
cookie-servers	8	ipv4-address	true	false
lpr-servers	9	ipv4-address	true	false
impress-servers	10	ipv4-address	true	false
resource-location-servers	11	ipv4-address	true	false
boot-size	13	uint16	false	false
merit-dump	14	string	false	false
domain-name	15	fqdn	false	true
swap-server	16	ipv4-address	false	false
root-path	17	string	false	false
extensions-path	18	string	false	false
ip-forwarding	19	boolean	false	false
non-local-source-routing	20	boolean	false	false
policy-filter	21	ipv4-address	true	false
max-dgram-reassembly	22	uint16	false	false
default-ip-ttl	23	uint8	false	false
path-mtu-aging-timeout	24	uint32	false	false
path-mtu-plateau-table	25	uint16	true	false
interface-mtu	26	uint16	false	false
all-subnets-local	27	boolean	false	false
broadcast-address	28	ipv4-address	false	false
perform-mask-discovery	29	boolean	false	false
mask-supplier	30	boolean	false	false
router-discovery	31	boolean	false	false
router-solicitation-address	32	ipv4-address	false	false
static-routes	33	ipv4-address	true	false
trailer-encapsulation	34	boolean	false	false
arp-cache-timeout	35	uint32	false	false
ieee802-3-encapsulation	36	boolean	false	false
default-tcp-ttl	37	uint8	false	false
tcp-keepalive-interval	38	uint32	false	false
tcp-keepalive-garbage	39	boolean	false	false
nis-domain	40	string	false	false
nis-servers	41	ipv4-address	true	false
ntp-servers	42	ipv4-address	true	false
vendor-encapsulated-options	43	empty	false	false
netbios-name-servers	44	ipv4-address	true	false
netbios-dd-server	45	ipv4-address	true	false
netbios-node-type	46	uint8	false	false
netbios-scope	47	string	false	false
font-servers	48	ipv4-address	true	false
x-display-manager	49	ipv4-address	true	false
dhcp-option-overload	52	uint8	false	false
dhcp-message	56	string	false	false
dhcp-max-message-size	57	uint16	false	false
vendor-class-identifier	60	binary	false	false
nwip-domain-name	62	string	false	false
nwip-suboptions	63	binary	false	false
tftp-server-name	66	string	false	false
boot-file-name	67	string	false	false
user-class	77	binary	false	false
client-system	93	uint16	true	false
client-ndi	94	record (uint8, uint8, uint8)	false	false
uuid-guid	97	record (uint8, binary)	false	false
subnet-selection	118	ipv4-address	false	false
domain-search	119	binary	false	false
vivco-suboptions	124	binary	false	false
vivso-suboptions	125	binary	false	false

DHCP Option Types

binary:

An arbitrary string of bytes, specified as a set of hexadecimal digits.

boolean:

Boolean value with allowed values true or false.

empty:

No value, data is carried in suboptions.

fqdn:

Fully qualified domain name (e.g. www.example.com).

ipv4-address:

IPv4 address in dotted-decimal notation (e.g. 192.0.2.1).

ipv6-address:

IPv6 address in compressed colon notation (e.g. 2001:db8::1).

record:

Structured data of other types (except record and empty).

string:

Any arbitrary text.

int32:

32 bit signed integer with values between -2147483648 and 2147483647.

uint8:

8 bit unsigned integer with values between 0 and 255.

uint16:

16 bit unsigned integer with values between 0 and 65535.

uint32:

32 bit unsigned integer with values between 0 and 4294967295.