dhcpcd.conf

Name:

/etc/dhcpcd.conf

Description:

Although dhcpcd can do everything from the command line, there are cases where it's easier to do it once in a configuration file. Most of the options found in dhcpcd can be used here. The first word on the line is the option, and the rest of the line is the value. Leading and trailing whitespace for the option and value are trimmed. You can escape characters in the value using the \ character. Comments can be prefixed with the # character. String values should be quoted with the " character.

Here's a list of available options:

allowinterfaces pattern

When discovering interfaces, the interface name must match the specified pattern, which is a space- or comma-separated list of patterns passed to fnmatch(). If the same interface is matched in denyinterfaces, then it is still denied.

denyinterfaces pattern

When discovering interfaces, the interface name must not match the specified pattern, which is a space- or comma-separated list of patterns passed to fnmatch().

anonymous

Enable Anonymity Profiles for DHCP, RFC 7844. Any DUID is ignored and ClientID is set to LL only. All non-essential options are then masked at this point, but they could be unmasked by explicitly requesting the option after anonymous is processed. As such, anonymous should be the last option in the configuration unless you really want to send something that could identify you. The dhcpcd utility does not try to reboot an old lease; it goes straight into DISCOVER/SOLICIT.

randomise_hwaddr

Forces a hardware address randomisation when the interface is brought up or when the carrier is lost. This option is generally used in tandem with anonymous.

arping address [address]

Instruct dhcpcd to arping each address in order before attempting DHCP. If an address is found, the replying hardware address is selected as the profile; otherwise, the IP address.

For example:

interface bge0
arping 192.168.0.1
# My specific 192.168.0.1 network
profile dd:ee:aa:dd:bb:ee
static ip_address=192.168.0.10/24
# A generic 192.168.0.1 network
profile 192.168.0.1
static ip_address=192.168.0.98/24
    

authprotocol protocol [algorithm [rdm]

Authenticate DHCP messages. See the Supported Authentication Protocols section. If the specified protocol is token, then the specified algorithm is snd_secretid/rcv_secretid so that you can send and receive different tokens.

authtoken secretid realm expire key

Define a shared key for use in authentication. The realm can be in quotes ("") to use with the protocol specified by delayed. The expire value is the date the token expires and should be formatted as "yyy-mm-dd HH:MM". You can use the keyword forever or 0, which means the token never expires. For the token protocol, secretid needs to be 0 and realm needs to be "". If dhcpcd has the error dhcp_auth_encode: Invalid argument, it means that dhcpcd could not find the correct authentication token in your configuration.

background

Fork to the background immediately. This is useful for startup scripts that don't disable link messages for carrier status.

blacklist address [/cidr]

Ignores all packets from the specified address.

whitelist address [/cidr]

Only accept packets from the specified address. If whitelist and blacklist specify the same address, the address is accepted.

bootp

Be a BOOTP client. Basically, this option configures dchpcd to not send a DHCP Message Type option and to only interact with a BOOTP server. All other DHCP options still work.

broadcast

Instruct the DHCP server to broadcast replies back to the client. Normally this is only set for non-Ethernet interfaces, such as FireWire and InfiniBand. In most cases, dhcpcd sets this automatically.

controlgroup group

Sets the group ownership of /var/run/dhcpcd/sock so that users other than root can connect to dhcpcd.

debug

Echo debug messages to stderr and system log.

dev value

Load the specified /dev management module. The dhcpcd loads the first one found to work, if any.

env value

Push the specified value to the environment for use in dhcpcd-run-hooks. For example, you can force the hostname hook to always set the hostname with env force_hostname=YES. Or, to set which driver wpa_supplicant should use, use env wpa_supplicant_driver=nl80211.

If the hostname is set, it is set to the FQDN if possible as per RFC 4702, section 3.1. If the FQDN option is missing,dhcpcd still tries to set a FQDN from the hostname and domain options for consistency. To override this behavior, specify the option with the following format:

env hostname_fqdn=[ YES|NO|SERVER ]

Where SERVER means just what the server says, don't manipulate it. This could lead to an inconsistent hostname on a DHCPv4 and DHCPv6 network where the DHCPv4 hostname is short and the DHCPv6 has an FQDN. DHCPv6 has no hostname option.

clientid string

Send the specified client ID. If the string is of the format 01:02:03, it is encoded as hex. For interfaces whose hardware address is longer than 8 bytes, or if the value is an empty string, dhcpcd sends a default client ID of the hardware family and the hardware address.

duid [ ll|lt| uuid|value]

Use a DHCP Unique Identifier. If a system UUID is available, that is used to create a DUID-UUID. If no system UUID is available and persistent storage is available, a DUID-LLT (link local address + time) is generated; otherwise, DUID-LL is generated (link local address). The DUID type can be hinted as an optional parameter if the file /var/db/duid does not exist. If none of ll, lt, or uuid is specified, value is converted from 00:11:22:33 format. This value, plus the IAID is used as the clientid value. The DUID generated is held in /var/db/duid and should not be copied to other hosts. This file also takes precedence over the above rules except for setting a value.

iaid iaid

Set the Interface Association Identifier to the specified value. This option must be used in an interface block. This value defaults to the VLANID (prefixed with 0xff) for the interface if set; otherwise, the last 4 bytes of the hardware address assigned to the interface. Each instance of this should be unique within the scope of the client and dhcpcd warns if a conflict is detected. If there is a conflict, it is only a problem if the conflicted IAIDs are used on the same network.

dhcp

Enable DHCP on the interface, on by default.

dhcp6

Enable DHCPv6 on the interface, on by default.

ipv4

Enable IPv4 on the interface, on by default.

ipv6

Enable IPv6 on the interface, on by default.

request [address]

Request the specified address in the DHCP DISCOVER message. There is no guarantee this is the address the DHCP server will actually give. If no address is given, the first address currently assigned to the interface specified by interface is used.

inform [address [cidr[broadcast_address]]]

Behaves like request, but sends a DHCP INFORM instead of DISCOVER/REQUEST. This option does not get a lease as such, just notifies the DHCP server of the address in use. You should also include the optional cidr network number in case the address is not already configured on the interface. The dhcpcd utility remains running and pretends it has an infinite lease. It does not de-configure the interface when it exits. If dhcpcd fails to contact a DHCP server, it returns a failure instead of falling back on IPv4LL.

inform6

Performs a DHCPv6 Information Request. No address is requested or specified, but all other DHCPv6 options are allowed. This is normally performed automatically when an IPv6 Router Advertisement indicates that the client should perform this operation. This option is only needed when dhcpcd is not processing IPv6 RA messages and the need for a DHCPv6 Information Request exists.

persistent

The dhcpcd utility normally de-configures the interface and configuration when it exits. Sometimes, this isn't desirable if, for example, you have root mounted over NFS or SSH clients connect to this host and they need to be notified of the host shutting down. You can use this option to stop this action from happening.

fallback profile

Fall back to using this profile if DHCP fails. This option allows you to configure a static profile instead of using ZeroConf.

hostname name

Sends the specified hostname to the DHCP server so it can be registered in DNS. If the specified name is an empty string, then the current system hostname is sent. If the name is a FQDN (i.e., contains a "."), then that's how it's encoded.

hostname_short

Sends the short hostname to the DHCP server instead of the FQDN, which is useful because DHCP servers do not register the FQDN in their DNS if the domain part does not match theirs.

Also, see env to control how the hostname is set on the host.

ia_na [iaid[/address]]

Request a DHCPv6 Normal Address for the specified Identity Association Identifier (IAID). The ID defaults to the one specified by iaid. You can request more than one DHCPv6 Normal Address by specifying a unique IAID for each one.

ia_ta [iaid]

Request a DHCPv6 Temporary Address for the specified IAID. You can request more than one DHCPv6 Temporary Address by specifying a unique IAID for each one.

ia_pd [iaid [/ prefix / prefix_len] [interface [/ sla_id [/ prefix_len [/ suffix]]]]]

Request a DHCPv6 Delegated Prefix for the specified IAID. This option must be used in an interface block. Unless sla_id is 0 with the same resultant prefix length as the delegation, a reject route is installed for the Delegated Prefix to stop unallocated addresses being resolved upstream. If no interface is given, a prefix is assigned to every other interface with a sla_id equivalent to the interface index assigned by io-sock. Otherwise, addresses are only assigned for each interface and sla_id. Each assigned address has a suffix, defaulting to 1. If the suffix is 0, a stateless address autoconfiguration (SLAAC) address is assigned. You cannot assign a prefix to the requesting interface unless the DHCPv6 server supports the RFC 6603 Prefix Exclude Option. The dhcpcd utility has to be running for all the interfaces it is delegating to. A default prefix_len of 64 is assumed, unless the maximum sla_id does not fit. In this case, prefix_len is increased to the highest multiple of 8 that can accommodate the sla_id. The sla_id value is an integer that must be unique inside the iaid and is added to the prefix, which must fit inside prefix_len less the length of the delegated prefix. You can specify multiple interface, sla_id, and prefix_len values per ia_pd, space separated. IPv6RS should be disabled globally when requesting a Prefix Delegation.

In the following example, eth0 is the externally facing interface to be configured for both IPv4 and IPv6. The DHCPv4 server provides an IPv4 address and a default route. The DHCPv6 server provides an IPv6 address, a default route and a /64 subnet to be delegated to the internal interface. The eth1 interface is automatically configured for IPv6 using the first address (::1) from the delegated prefix. A second prefix is requested and assigned to two other interfaces. The rtadvd utility can be used with an empty configuration file on eth1, eth2, and eth3, to provide automatic IPv6 address configuration for the internal network.

noipv6rs                 # disable routing solicitation
denyinterfaces eth2      # Don't touch eth2 at all
interface eth0
  ipv6rs                 # enable routing solicitation for eth0
  ia_na 1                # request an IPv6 address
  ia_pd 2 eth1/0         # request a prefix delegation and assign it to eth1
  ia_pd 3 eth2/1 eth3/2  # request a prefix delegation and assign it to eth2 and eth3

ipv4only

Only configure IPv4.

ipv6only

Only configure IPv6.

fqdn [ disable | none | ptr | both ]

Specify none to not ask the DHCP server to update DNS. Specify ptr to ask the DHCP server to update the PTR record of the host in DNS, or both to update both the PTR and A records. Specify disable to disable the FQDN option. The default is both. The dhcpcd utility itself never does any DNS updates, and it encodes the FQDN hostname as specified in RFC 1035.

interface interface

Parse subsequent options for the specified interface only.

ipv6ra_autoconf

Generate SLAAC addresses for each prefix advertised by an IPv6 Router Advertisement message with the Auto flag set. On by default.

ipv6ra_noautoconf

Disables ipv6ra_autoconf.

ipv6ra_fork

Make dhcpcd always fork on a IPv6 Router Advertisement (RA). By default, when dhcpcd receives an RA, it only forks to the background if the RA contains at least one unexpired RDNSS option and a valid prefix or no DHCPv6 instruction.

ipv6rs

Enable IPv6 Router Advertisement solicitation. This setting is on by default, but this option allows you to enable it for one interface in cases where it is disabled globally.

leasetime seconds

Set a lease time of the specified number of seconds. Specify -1 to set an infinite lease time. By default, dhcpcd does not request any lease time and DHCP server sets it. It is not possible to request a DHCPv6 lease time as this is not RFC compliant. See RFC 8415 21.4, 21.6, 21.21 and 21.22.

link_rcvbuf size

Override the size of the link receive buffer from the io-sock default. While dhcpcd recovers from link buffer overflows, this may not be desirable on heavily loaded systems.

logfile logfile

Write to the specified log file. The dhcpcd still writes to the system log. The log file is reopened when dhcpcd receives the SIGUSR2 signal.

metric metric

Use the specified metric to prefer an interface over another one, lowest wins. The dhcpcd utility supplies a default metric of 1000 + if_nametoindex(). This value is offset by 2000 for wireless interfaces, with additional offsets of 1000000 for IPv4LL and 2000000 for roaming interfaces.

mudurl url

Specify the URL for a Manufacturer Usage Description (MUD). The description is used by upstream network devices to instantiate any desired access lists. For more information, see documentation provided by the Internet Engineering Task Force (e.g., draft-ietf-opsawg-mud-tls-12).

noalias

Remove any pre-existing IPv4 addresses from the interface when adding a new IPv4 address.

noarp

Don't send any ARP requests. This option also disables IPv4LL.

noauthrequired

Don't require authentication even though dhcpcd requests it. Also allows FORCERENEW and RECONFIGURE messages without authentication.

nodelay

Don't delay for an initial randomised time when starting protocols.

nodev

Don't load /dev management modules.

nodhcp

Don't start DHCP or listen to DHCP messages. This option is only useful when you allow IPv4LL.

nodhcp6

Don't start DHCPv6 or listen to DHCPv6 messages. Normally DHCPv6 is started by an IPv6 Router Advertisement instruction or configuration.

nogateway

Don't install any default routes.

gateway

Install a default route if available (default).

nohook script

Don't run this hook script. Matches full name, or prefixed with 2 numbers optionally ending with .sh. Do the following to stop dhcpcd from touching your DNS settings or starting wpa_supplicant:

nohook resolv.conf, wpa_supplicant

noipv4

Don't attempt to configure an IPv4 address.

noipv4ll

Instruct dhcpcd to not attempt to obtain an IPv4LL address if it fails to get one via DHCP. See RFC 3927.

noipv6

Don't solicit or accept IPv6 Router Advertisements and DHCPv6.

noipv6rs

Don't solicit or accept IPv6 Router Advertisements.

nolink

Don't receive link messages about carrier status.

noup

Don't bring the interface up when in manager mode.

option option

Requests the option from the server. It can be a variable to be used in dhcpcd-run-hooks or the numerical value. You can specify more options separated by commas, spaces or more option lines. Prepend dhcp6_ to option to request a DHCPv6 option. If no DHCPv6 options are configured, then DHCPv4 options are mapped to the equivalent DHCPv6 options.

Prepend nd_ to option to handle ND options, but this only works for nooption, reject, and require options.

To see a list of options you can use, call dhcpcd with -V or --variables.

nooption option

Remove the option from the message before it's processed.

require option

Requires the specified option to be present in all messages; otherwise, the message is ignored. To enforce that dhcpcd only responds to DHCP servers and not BOOTP servers, you can require dhcp_message_type. This isn't an exact science though because a BOOTP server can send DHCP-like options.

reject option

Reject a message that contains the specified option. This option is useful when you cannot use require to select or de-select BOOTP messages.

destination option

If dhcpcd.conf detects an address added to a point to point interface (PPP, TUN, etc.), it sets the listed DHCP options to the destination address of the interface.

profile name

Parse subsequent options for the specified profile only.

quiet

Suppress any dhcpcd output to the console, except for errors.

reboot seconds

Wait the specified number of seconds before moving to the DISCOVER phase if dhcpcd has an old lease to use. Wait the specified number of seconds before starting fallback states from the DISCOVER phase. IPv4LL is started when the first reboot timeout is reached. The default is 5 seconds. A setting of 0 seconds causes dhcpcd.conf to skip the reboot phase and go straight into DISCOVER. This behavior is desirable for mobile users because if you change from network A to network B and they use the same subnet and the address from network A isn't in use on network B, then the DHCP server remains silent even if authoritative, which means dhcpcd times out before moving back to the DISCOVER phase. This option has no effect on DHCPv6 other than skipping the reboot phase.

release

Release the lease prior to stopping the interface.

script script

Use the specified script instead of the default one (/usr/lib/dhcpcd/dhcpcd-run-hooks).

ssid ssid

Parse subsequent options for the specified wireless SSID only.

slaac hwaddr | private [ temp | temporary]

Set the interface identifier used for SLAAC generated IPv6 addresses. If private is specified, a RFC 7217 address is generated. If temporary is specified, a temporary address is created for the prefix.

static value

Configure a static value. If you set ip_address, dhcpcd won't attempt to obtain a lease and just uses the value for the address with an infinite lease time. If you set ip6_address, dhcpcd continues auto-configuration as normal.

The following example configures two static addresses, an IPv4 router, DNS and disables IPv6 auto-configuration. You could also use the inform6 command here to obtain more information via DHCPv6. For IPv4, you should use the inform ipaddress option instead of setting a static address.

interface eth0
noipv6rs
static ip_address=192.168.0.10/24
static broadcast_address=192.168.0.63
static ip6_address=fd51:42f8:caae:d92e::ff/64
static routers=192.168.0.1
static domain_name_servers=192.168.0.1 fd51:42f8:caae:d92e::1

The following example for PPP gives the destination a default route. It uses the special destination keyword to insert the destination address into the value.

interface ppp0
static ip_address=
destination routers

timeout seconds

Time out after the specified number of seconds, instead of the default 30. A setting of 0 seconds causes dhcpcd to wait forever to get a lease. If dhcpcd is working on a single interface then dhcpcd exits when a timeout occurs; otherwise, dhcpcd forks into the background. If using IPv4LL, dhcpcd starts the IPv4LL process after the timeout and then waits a little longer before really timing out.

userclass string

Tag the DHCPv4 message with the specified userclass. You can specify more than one.

msuserclass string

Tag the DHCPv4 message with the Microsoft userclass. Unlike userclass, this option can only be added once. It should only be used for Microsoft DHCP servers and the vendorclassid should be set to MSFT 98 or MSFT 5.0. This option is not RFC compliant.

vendor code,value

Add an encapsulated vendor option. The value of code should be between 1 and 254 inclusive. To add a raw vendor string, omit code but keep the comma.

Examples:

Set the vendor option 01 with an IP address:

vendor 01,192.168.0.2

Set the vendor option 02 with a hex code:

vendor 02,01:02:03:04:05

Set the vendor option 03 with an IP address as a string:

vendor 03,\"192.168.0.2\"

Set un-encapsulated vendor option to hello world.

vendor ,"hello world"

vendorclassid string

Set the DHCP Vendor Class. DHCPv6 has its own option, as shown below. The default format is: dhcpcd-version:os:machine:platform. For example:

dhcpcd-5.5.6:NetBSD-6.99.5:i386:i386

If not set, none is sent. Some badly configured DHCP servers reject unknown vendor class IDs. To work around it, try and impersonate Windows by using the MSFT vendor class ID.

vendclass en data

Add the DHCPv4 Vendor Identifying Vendor Class with the IANA-assigned Enterprise Number specified by en with the specified data. This option can be set more than once to add more data, but the behaviour, as per RFC(3925), is undefined if the Enterprise Number differs.

waitip [4 | 6]

Wait for an address to be assigned before forking to the background. 4 means wait for an IPv4 address to be assigned. 6 means wait for an IPv6 address to be assigned. If no argument is given, dhcpcd.conf will wait for any address protocol to be assigned. It is possible to wait for more than one address protocol and dhcpcd.conf will only fork to the background when all waiting conditions are satisfied.

xidhwaddr

Use the last four bytes of the hardware address as the DHCP XID instead of a randomly generated number.

Defining new options

DHCP, ND and DHCPv6 allow for the use of custom options. Each option needs to be started with the define or define6 directive. This initial directive can optionally be followed by both embed or encap options. Both can be specified more than once, and embed must come before encap.

definecodetypevariable

Defines the DHCP option code of type with a name of variable exported to dhcpcd-run-hooks.

definendcodetypevariable

Defines the ND option code of type with a name of variable exported todhcpcd-run-hooks with a prefix of nd_.

define6codetypevariable

Defines the DHCPv6 option code of type with a name of variable exported to dhcpcd-run-hooks with a prefix of dhcp6_.

vendoptcodetypevariable

Defines the Vendor-Identifying Vendor Options. The code is the IANA Enterprise Number which will uniquely describe the encapsulated options. type is normally encap. variable names the Vendor option to be exported.

embedtypevariable

Defines an embedded variable within the defined option. The length is determined by the specified type. If the variable is not the same as defined in the parent option, it is prefixed with the parent variable first with an underscore. The variable is not processed if it has the name of reserved.

encapcodetypevariable

Defines an encapsulated variable within the defined option. The length is determined by the type. If the variable is not the same as defined in the parent option, it is prefixed with the parent variable first with an underscore.

Type Prefix

These keywords come before the type itself, to describe it more fully. You can use more than one, but they must appear in the order listed below.

request

Requests the option by default without having to be specified in user configuration.

norequest

This option cannot be requested, regardless of user configuration.

optional

This one is optional. Only makes sense for embedded options like the client FQDN option.

index

The option can appear more than once, and is indexed.

array

The option data is split into a space separated array, with each element being the same type.

Types to define

The type directly affects the length of data consumed inside the option. Any remaining data is normally discarded. Lengths can be specified for string and binhex types, but this is generally with other data embedded afterwards in the same option.

ipaddress

An IPv4 address (4 bytes).

ip6address

An IPv6 address (16 bytes).

string [: length]

A NVT ASCII string of printable characters.

byte

A byte.

bitflags : flags

A byte represented as a string of flags, with the most significant bit placed first. For example, if using the string ABCDEFGH, A would equal 10000000, B 01000000, C 00100000, etc. If the bit is not set, the flag is not printed. A flag of 0 is not printed even if the bit position is set. This is to reserve the first bits while the last bits are being assigned.

int16

A signed 16bit integer (2 bytes).

unit16

An unsigned 16bit integer (2 bytes).

int32

A signed 32bit integer (4 bytes).

uint32

An unsigned 32bit integer (4 bytes).

flag

A fixed value (1) to indicate that the option is present (0 bytes).

domain

An RFC 3397 encoded string.

dname

An RFC 1035 validated string.

binhex [: length]

Binary data expressed as hexadecimal.

embed

Contains embedded options (implies encap as well).

encap

Contains encapsulated options (implies embed as well).

option

References an option from the global definition.

Example Definition

# DHCP option 81, Fully Qualified Domain Name, RFC 4702
define 81 embed fqdn
embed byte flags
embed byte rcode1
embed byte rcode2
embed domain fqdn

# DHCP option 125, Vendor Specific Information Option, RFC 3925
define 125 encap vsio
embed uint32 enterprise_number
# Options defined for the enterprise number
encap 1 ipaddress ipaddress
  

Supported Authentication Protocols

token

Sends a plain text token the server expects and matches it with a token sent by the server. The tokens do not have to be the same. If unspecified, the token with a secretid of 0 will be used in sending messages and validating received messages.

delayedrealm

Delayed Authentication. dhcpcd will send an authentication option with no key or MAC. The server will see this option, and select a key for dhcpcd.conf , writing the realm and secretid in it. dhcpcd looks for an unexpired token with a matching realmand secretid. This token is used to authenticate all other messages.

delayed

Same as delayedrealm but without a realm.

Supported Authentication Algorithms

If no algorithms are specified, hmac-md5 is the default.

hmac-md5

Supported Replay Detection Mechanisms

If none specified, monotonic is the default. If this is changed from what was previously used, or the means of calculating or storing it is broken, then the DHCP server resets its notion of the client's Replay Detection Value reset.

monocounter

Read the number in the file /var/db/dhcpcd-rdm.monotonic and add one to it.

monotime

Create an NTP timestamp from the system time.

monotonic

Same as monotime

Contributing author: