Ubuntu Manpage: dhcpcd.conf — dhcpcd configuration file

Provided by: dhcpcd-base_10.1.0-12_amd64

NAME

       dhcpcd.conf — dhcpcd configuration file

DESCRIPTION

Although dhcpcd can do everything from the command line, there are cases where it's just easier to do it
once in a configuration file. Most of the options found in dhcpcd(8) 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 pattern which is a space or comma
separated list of patterns passed to fnmatch(3). If the same interface is matched in
denyinterfaces then it is still denied.

denyinterfaces pattern
When discovering interfaces, the interface name must not match pattern which is a space or comma
separated list of patterns passed to fnmatch(3).

anonymous
Enables 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 the anonymous option is processed. As such, the anonymous
option should be the last option in the configuration unless you really want to send something
which could identify you. dhcpcd will not try and reboot an old lease, it will go straight into
DISCOVER/SOLICIT.

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

arping address [address]
dhcpcd will arping each address in order before attempting DHCP. If an address is found, we will
select the replying hardware address as the profile, otherwise the IP address. 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 protocol is
token then algorithm is snd_secretid/rcv_secretid so you can send and receive different tokens.

authtoken secretid realm expire key
Define a shared key for use in authentication. realm can be "" to for use with the delayed
protocol. expire is the date the token expires and should be formatted "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
then 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 which don't disable link
messages for carrier status.

blacklist address[/cidr]
Ignores all packets from address[/cidr].

whitelist address[/cidr]
Only accept packets from address[/cidr]. blacklist is ignored if whitelist is set.

bootp Be a BOOTP client. Basically, this just doesn't send a DHCP Message Type option and will only
interact with a BOOTP server. All other DHCP options still work.

broadcast
Instructs 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 will set this
automatically.

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

debug Echo debug messages to the stderr and syslog.

dev value
Load the value /dev management module. dhcpcd will load the first one found to work, if any.

env value
Push value to the environment for use in dhcpcd-run-hooks(8). For example, you can force the
hostname hook to always set the hostname with env force_hostname=YES. Or set which driver
wpa_supplicant(8) should use with env wpa_supplicant_driver=nl80211

If the hostname is set, it will be will set to the FQDN if possible as per RFC 4702, section 3.1.
If the FQDN option is missing, dhcpcd will still try and set a FQDN from the hostname and domain
options for consistency. To override this, set env hostname_fqdn=[YES|NO|SERVER]. A value of
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 clientid. If the string is of the format 01:02:03 then it is encoded as hex. For
interfaces whose hardware address is longer than 8 bytes, or if the clientid is an empty string
then dhcpcd sends a default clientid 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 will be used to create a DUID-
UUID, otherwise if persistent storage is available then 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/lib/dhcpcd/duid does not exist. If not ll, lt or uuid
then value will be converted from 00:11:22:33 format. This, plus the IAID will be used as the
clientid. The DUID generated will be held in /var/lib/dhcpcd/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 iaid. This option must be used in an interface
block. This 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 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 then the first address currently assigned
to the interface is used.

inform [address[/cidr[/broadcast_address]]]
Behaves like request as above, but sends a DHCP INFORM instead of DISCOVER/REQUEST. This 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. dhcpcd remains running and pretends it has an infinite lease. dhcpcd will not de-
configure the interface when it exits. If dhcpcd fails to contact a DHCP server then 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
dhcpcd 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 from happening.

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

fallback_time seconds
Start fallback after seconds. The default is 5 seconds.

hostname name
Sends the hostname name to the DHCP server so it can be registered in DNS. If name is an empty
string then the current system hostname is sent. If name is a FQDN (i.e., contains a .) then it
will be encoded as such.

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

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

ia_na [iaid [/ address]]
Request a DHCPv6 Normal Address for iaid. iaid defaults to the iaid option as described above.
You can request more than one ia_na by specifying a unique iaid for each one.

ia_ta [iaid]
Request a DHCPv6 Temporary Address for iaid. You can request more than one ia_ta 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 iaid. This option must be used in an interface block.
Unless a sla_id of 0 is assigned 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 then we will assign a prefix to every other interface with a
sla_id equivalent to the interface index assigned by the OS. Otherwise addresses are only
assigned for each interface and sla_id. To avoid delegating to any interface, use - as the
invalid interface name. Each assigned address will have a suffix, defaulting to 1. If the
suffix is 0 then a SLAAC address is assigned. You cannot assign a prefix to the requesting
interface unless the DHCPv6 server supports the RFC 6603 Prefix Exclude Option. dhcpcd 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. sla_id is an integer which 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 / prefix_len 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 will provide us with an IPv4 address and a default route. The
DHCPv6 server is going to provide us with an IPv6 address, a default route and a /64 subnet to be
delegated to the internal interface. The eth1 interface will be automatically configured for
IPv6 using the first address (::1) from the delegated prefix. A second prefix is requested and
assigned to two other interfaces. rtadvd(8) 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 PD and assign it to eth1
ia_pd 3 eth2/1 eth3/2 # req a PD and assign it to eth2 and eth3
ia_pd 4 - # request a PD but don't assign it

ipv4only
Only configure IPv4.

ipv6only
Only configure IPv6.

fqdn [disable | none | ptr | both]
none will not ask the DHCP server to update DNS. ptr just asks the DHCP server to update the PTR
record of the host in DNS, whereas both also updates the A record. disable will disable the FQDN
option. The default is both. dhcpcd itself never does any DNS updates. dhcpcd encodes the FQDN
hostname as specified in RFC 1035.

interface interface
Subsequent options are only parsed for this interface.

ipv4ll_time seconds
Wait for seconds before starting IPv4LL. The default is 5 seconds.

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 the above option.

ipv6ra_fork
By default, when dhcpcd receives an IPv6 Router Advertisement, dhcpcd will only fork to the
background if the RA contains at least one unexpired RDNSS option and a valid prefix or no DHCPv6
instruction. Set this option so to make dhcpcd always fork on a RA.

ipv6rs Enables IPv6 Router Advertisement solicitation. This is on by default, but is documented here in
the case where it is disabled globally but needs to be enabled for one interface.

leasetime seconds
Request DHCP a lease time of seconds. -1 represents an infinite lease time. By default dhcpcd
does not request any lease time and leaves it in the hands of the DHCP server. 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 kernel default. While dhcpcd will recover
from link buffer overflows, this may not be desirable on heavily loaded systems.

logfile logfile
Writes to the specified logfile. dhcpcd still writes to syslog(3). The logfile is reopened when
dhcpcd receives the SIGUSR2 signal.

metric metric
Metrics are used to prefer an interface over another one, lowest wins. dhcpcd will supply a
default metric of 1000 + if_nametoindex(3). This will be offset by 2000 for wireless interfaces,
with additional offsets of 1000000 for IPv4LL and 2000000 for roaming interfaces.

mudurl url
Specifies the URL for a Manufacturer Usage Description (MUD). The description is used by
upstream network devices to instantiate any desired access lists. See draft-ietf-opsawg-mud for
more information.

noalias
Any pre-existing IPv4 addresses will be removed from the interface when adding a new IPv4
address.

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

arp_persistdefence
Keep the IP address even if defence fails upon IP Address conflict.

noauthrequired
Don't require authentication even though we requested 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 is only useful when allowing 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.

So to stop dhcpcd from touching your DNS settings or starting wpa_supplicant you would do:-
nohook resolv.conf, wpa_supplicant

noipv4 Don't attempt to configure an IPv4 address.

noipv4ll
Don't attempt to obtain an IPv4LL address if we failed 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. You should only set this for buggy interface
drivers.

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(8) 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 equivalent DHCPv6 options.

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

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

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

require option
Requires the 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 option. This is useful when you cannot use require to select
/ de-select BOOTP messages.

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

profile name
Subsequent options are only parsed for this profile name.

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

reboot seconds
Allow reboot seconds before moving to the DISCOVER phase if we have an old lease to use. Allow
reboot 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 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 will remain silent even if
authoritative which means dhcpcd will timeout before moving back to the DISCOVER phase. This has
no effect on DHCPv6 other than skipping the reboot phase.

release
dhcpcd will release the lease prior to stopping the interface.

script script
Use script instead of the default /usr/lib/dhcpcd/dhcpcd-run-hooks.

request_time seconds
Request the lease for seconds before going back to DISCOVER. The default is 180 seconds.

ssid ssid
Subsequent options are only parsed for this wireless ssid.

slaac hwaddr | private | token token [temp | temporary]
Selects the interface identifier used for SLAAC generated IPv6 addresses. If private is used, a
RFC 7217 address is generated. If token token is used then the token is combined with the prefix
to make the final address. The temporary directive will create a temporary address for the
prefix as well.

static value
Configures a static value. If you set ip_address then dhcpcd will not attempt to obtain a lease
and will just use the value for the address with an infinite lease time. If you set an empty
value this removes all prior static allocations to the same value. This is useful when using
profiles and in the case of ip_address it will remove the static allocation. Note that setting
0.0.0.0 keeps the static allocation but waits for a 3rdparty to configure the address. If you
set ip6_address, dhcpcd will continue auto-configuration as normal.

Here is an example which configures two static address, overriding the default IPv4 broadcast
address, an IPv4 router, DNS and disables IPv6 auto-configuration. You could also use the
inform6 command here if you wished 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

Here is an example for PPP which 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=0.0.0.0
destination routers

timeout seconds
Time out after 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 will exit when a
timeout occurs, otherwise dhcpcd will fork into the background. If using IPv4LL then dhcpcd
start the IPv4LL process after the timeout and then wait a little longer before really timing
out.

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

msuserclass string
Tag the DHCPv4 mesasge with the Microsoft userclass. Unlike the userclass option, this one 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. 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 is
dhcpcd-<version>:<os>:<machine>:<platform>. For example
dhcpcd-5.5.6:NetBSD-6.99.5:i386:i386
If not set then none is sent. Some badly configured DHCP servers reject unknown vendorclassids.
To work around it, try and impersonate Windows by using the MSFT vendorclassid.

vendclass en data
Add the DHCPv6 Vendor Indetifying Vendor Class with the IANA assigned Enterprise Number en with
the 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, and RFC 3925 vendor options for DHCP can also be
supplied. Each option needs to be started with the define, definend, define6 or vendopt directive. This
can optionally be followed by both embed or encap options. Both can be specified more than once and
embed must come before encap.

define code type variable
Defines the DHCP option code of type with a name of variable exported to dhcpcd-run-hooks(8).

definend code type variable
Defines the ND option code of type with a name of variable exported to dhcpcd-run-hooks(8), with
a prefix of nd_.

define6 code type variable
Defines the DHCPv6 option code of type with a name of variable exported to dhcpcd-run-hooks(8),
with a prefix of dhcp6_.

vendopt code type variable
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.

embed type variable
Defines an embedded 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. If the variable has the name of reserved then it is not
processed.

encap code type variable
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 option is optional. Only makes sense for embedded options like the client FQDN option,
where the FQDN string itself is optional.

index The option can appear more than once and will be indexed.

array The option data is split into a space separated array, 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, most significant bit first. For example, using ABCDEFGH
then 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 allow
reservation of the first bits while assigning the last bits.

int16 A signed 16bit integer, 2 bytes.

uint16 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.

uri If an array then the first two bytes are the URI length inside the option data. Otherwise, the
whole option data is the URI. As a space is not allowed in the URI encoding, the URIs are space
separated.

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 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 will then look for an unexpired token with a matching realm and secretid. This
token is used to authenticate all other messages.

delayed Same as above, but without a realm.

Supported Authentication Algorithms
If none 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 will probably have to have its notion
of the client's Replay Detection Value reset.

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

monotime
Create an NTP timestamp from the system time.

monotonic
Same as monotime.

AUTHORS

       Roy Marples <roy@marples.name>

BUGS

       Please report them to https://roy.marples.name/projects/dhcpcd

Debian                                            May 24, 2024                                    DHCPCD.CONF(5)

NAME

DESCRIPTION

SEE ALSO

AUTHORS

BUGS