table of contents
DHCPCD.CONF(5) | File Formats Manual | DHCPCD.CONF(5) |
NAME¶
dhcpcd.conf
—dhcpcd
configuration file
DESCRIPTION¶
Althoughdhcpcd
can do everything from the
command line, there are cases where it's just easierto do it once in a
configuration file.Most of the options found
indhcpcd(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
matchpatternwhich is a space or comma separated list
of patterns passed tofnmatch(3).If the same interface is
matched in
denyinterfaces
then it is still denied. denyinterfaces
pattern- When discovering interfaces, the interface name must not matchpatternwhich is a space or comma separated list of patterns passed tofnmatch(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
optionafterthe
anonymous
option is processed.As such, theanonymous
optionshouldbe the last option in the configuration unless you really want tosend something which could identify you.dhcpcd
will not try and reboot an old lease, it will go straight intoDISCOVER/SOLICIT. randomise_hwaddr
- Forces a hardware address randomisation when the interface is brought upor 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 theprofile, otherwise the IP address.Example:interface bge0arping 192.168.0.1# My specific 192.168.0.1 networkprofile dd:ee:aa:dd:bb:eestatic ip_address=192.168.0.10/24# A generic 192.168.0.1 networkprofile 192.168.0.1static ip_address=192.168.0.98/24authprotocol
protocol[algorithm[rdm]]- Authenticate DHCP messages.See the Supported Authentication Protocols section.Ifprotocolistokenthenalgorithmissnd_secretid/rcv_secretid so you can send and receive different tokens.
authtoken
secretidrealmexpirekey- Define a shared key for use in
authentication.realmcan be "" to for use
with
thedelayedprotocol.expireis
the date the token expires and should be formatted "yyy-mm-dd
HH:MM".You can use the
keywordforeveror0which means
the token never expires.For the token
protocol,secretidneeds to be 0
andrealmneeds to be
"".If
dhcpcd
has the errordhcp_auth_encode: Invalid argumentthen it means thatdhcpcd
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 forcarrier status.
blacklist
address[/cidr]- Ignores all packets fromaddress[/cidr].
whitelist
address[/cidr]- Only accept packets
fromaddress[/cidr].
blacklist
is ignored ifwhitelist
is set. bootp
- Be a BOOTP client.Basically, this just doesn't send a DHCP Message Type option and will onlyinteract 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/sockso that
users other than root can connect to
dhcpcd
. debug
- Echo debug messages to the stderr and syslog.
dev
value- Load thevalue/devmanagement
module.
dhcpcd
will load the first one found to work, if any. env
value- Pushvalueto the environment for use
indhcpcd-run-hooks(8).For example, you can force the
hostname hook to always set the hostname
with
env
force_hostname=YES.Or set which driverwpa_supplicant(8)should use withenv
wpa_supplicant_driver=nl80211If the hostname is set, it will be will set to the FQDN if possible as perRFC 4702, section 3.1.If the FQDN option is missing,
dhcpcd
will still try and set a FQDN from the hostname and domain options forconsistency.To override this, setenv
hostname_fqdn=[YES|NO|SERVER].A value ofSERVERmeans just what the server says, don't manipulate it.This could lead to an inconsistent hostname on a DHCPv4 and DHCPv6 networkwhere the DHCPv4 hostname is short and the DHCPv6 has an FQDN.DHCPv6 has no hostname option. clientid
string- Send theclientid.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 theclientidis an empty
string then
dhcpcd
sends a defaultclientidof 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/duiddoes not exist.If
notll,ltoruuidthenvaluewill
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/duidand 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 toiaid.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 theinterface.Each instance of this should be unique within the scope of the client anddhcpcd
warns if a conflict is detected.If there is a conflict, it is only a problem if the conflicted IAIDs areused 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 theaddressin the DHCP DISCOVER message.There is no guarantee this is the address the DHCP server will actually give.If noaddressis given then the first address currently assigned to theinterfaceis 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 theaddressin use.You should also include the optionalcidrnetwork 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.Ifdhcpcd
fails to contact a DHCP server then it returns a failure instead of fallingback 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 Advertisementindicates 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 Requestexists. persistent
dhcpcd
normally de-configures the interface and configuration when it exits.Sometimes, this isn't desirable if, for example, you have root mounted overNFS or SSH clients connect to this host and they need to be notified ofthe 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.
hostname
name- Sends the hostnamenameto the DHCP server so it can be registered in DNS.Ifnameis an empty string then the current system hostname is sent.Ifnameis 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 theirDNS 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
foriaid.iaiddefaults to
the
iaid
option as described above.You can request more than one ia_na by specifying a uniqueiaidfor each one. ia_ta
[iaid]- Request a DHCPv6 Temporary Address foriaid.You can request more than one ia_ta by specifying a uniqueiaidfor each one.
ia_pd
[iaid[/prefix/prefix_len][interface[/sla_id[/prefix_len[/suffix]]]]]- Request a DHCPv6 Delegated Prefix foriaid.This
option must be used in an
interface
block.Unless asla_idof 0 is assigned with the same resultant prefix length as the delegation,a reject route is installed for the Delegated Prefix tostop unallocated addresses being resolved upstream.If nointerfaceis given then we will assign a prefix to every other interface with asla_idequivalent to the interface index assigned by the OS.Otherwise addresses are only assigned for eachinterfaceandsla_id.To avoid delegating to any interface, use - as the invalid interface name.Each assigned address will have asuffix,defaulting to 1.If thesuffixis 0 then a SLAAC address is assigned.You cannot assign a prefix to the requesting interface unless theDHCPv6 server supports theRFC 6603
Prefix Exclude Option.dhcpcd
has to be running for all the interfaces it is delegating to.A defaultprefix_lenof 64 is assumed, unless the maximumsla_iddoes not fit.In this caseprefix_lenis increased to the highest multiple of 8 that can accommodate thesla_id.sla_idis an integer which must be unique inside theiaidand is added to the prefix which must fit insideprefix_lenless the length of the delegated prefix.You can specify multipleinterface/sla_id/prefix_lenperia_pd
,space separated.IPv6RS should be disabled globally when requesting a Prefix Delegation.In the following example eth0 is the externally facing interface to beconfigured 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 defaultroute and a /64 subnet to be delegated to the internal interface.The eth1 interface will be automatically configuredfor 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 automaticIPv6 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]- nonewill not ask the DHCP server to update
DNS.ptrjust asks the DHCP server to update the
PTRrecord of the host in DNS, whereasbothalso
updates the A record.disablewill disable the FQDN
option.The default
isboth.
dhcpcd
itself never does any DNS updates.dhcpcd
encodes the FQDN hostname as specified inRFC 1035
. interface
interface- Subsequent options are only parsed for thisinterface.
ipv6ra_autoconf
- Generate SLAAC addresses for each Prefix advertised by an IPv6Router 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 unexpiredRDNSS option and a valid prefix or no DHCPv6 instruction.Set this option so to makedhcpcd
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 disabledglobally but needs to be enabled for one interface.
leasetime
seconds- Request DHCP a lease time
ofseconds.-1represents an
infinite lease time.By default
dhcpcd
does not request any lease time and leaves it in the hands of theDHCP 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
specifiedlogfile.
dhcpcd
still writes tosyslog(3).Thelogfileis reopened whendhcpcd
receives theSIGUSR2
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 offsetsof 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 anydesired access lists.See draft-ietf-opsawg-mud for more information.
noalias
- Any pre-existing IPv4 addresses will be removed from the interface whenadding a new IPv4 address.
noarp
- Don't send any ARP requests.This also disables IPv4LL.
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/devmanagement 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 orconfiguration.
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.SeeRFC 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 theoptionfrom the server.It can be a
variable to be used indhcpcd-run-hooks(8)or the
numerical value.You can specify moreoptionsseparated
by commas, spaces or more
option
lines.Prepend dhcp6_ tooptionto request a DHCPv6 option.If no DHCPv6 options are configured,then DHCPv4 options are mapped to equivalent DHCPv6 options.Prepend nd_ tooptionto handle ND options, but this only works for the
nooption
,reject
andrequire
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 theoptionto be present in all messages,
otherwise the message is ignored.To enforce
that
dhcpcd
only responds to DHCP servers and not BOOTP servers, you canrequire
dhcp_message_type.This isn't an exact science though because a BOOTP server can send DHCP-likeoptions. reject
option- Reject a message that contains theoption.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) thenit will set the listed DHCP options to the destination address of theinterface. profile
name- Subsequent options are only parsed for this profilename.
quiet
- Suppress any dhcpcd output to the console, except for errors.
reboot
seconds- Allowrebootseconds before moving to the DISCOVER
phase if we have an old lease to
use.Allowrebootseconds before starting fallback
states from the DISCOVER phase.IPv4LL is started when the
firstreboottimeout 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 tonetwork B and they use the same subnet and the address from network A isn'tin use on network B, then the DHCP server will remain silent even ifauthoritative which meansdhcpcd
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- Usescriptinstead of the default/usr/lib/dhcpcd/dhcpcd-run-hooks.
ssid
ssid- Subsequent options are only parsed for this wirelessssid.
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.Iftoken
tokenis used then the token is combined with the prefix to make the final address.Thetemporary
directive will create a temporary address for the prefix as well. static
value- Configures a staticvalue.If you
set
ip_address
thendhcpcd
will not attempt to obtain a lease and will just use the value for the addresswith an infinite lease time.If you set an empty value this removes all prior static allocations tothe same value.This is useful when using profiles and in the case ofip_address
it will remove the static allocation.Note that setting 0.0.0.0 keeps the static allocation but waits for a 3rdpartyto configure the address.If you setip6_address
,dhcpcd
will continue auto-configuration as normal.Here is an example which configures two static address, overriding the defaultIPv4 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 theinform
ipaddressoption instead of setting a static address.interface eth0noipv6rsstatic ip_address=192.168.0.10/24static broadcast_address=192.168.0.63static ip6_address=fd51:42f8:caae:d92e::ff/64static routers=192.168.0.1static domain_name_servers=192.168.0.1 fd51:42f8:caae:d92e::1Here is an example for PPP which gives the destination a default route.It uses the specialdestinationkeyword to insert the destination addressinto the value.
interface ppp0static ip_address=0.0.0.0destination routers timeout
seconds- Time out afterseconds,instead of the default 30.A
setting of
0secondscauses
dhcpcd
to wait forever to get a lease.Ifdhcpcd
is working on a single interface thendhcpcd
will exit when a timeout occurs, otherwisedhcpcd
will fork into the background.If using IPv4LL thendhcpcd
start the IPv4LL process after the timeout and then wait a little longerbefore 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 thevendorclassid
should be set to "MSFT 98" or "MSFT 5.0".This option is not RFC compliant. vendor
code,value- Add an encapsulated vendor option.codeshould be
between 1 and 254 inclusive.To add a raw vendor string,
omitcodebut keep the comma.Examples.
Set the vendor option 01 with an IP address.
vendor 01,192.168.0.2Set the vendor option 02 with a hex code.vendor 02,01:02:03:04:05Set 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
isdhcpcd-<version>:<os>:<machine>:<platform>.For
example
dhcpcd-5.5.6:NetBSD-6.99.5:i386:i386If 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
endata- Add the DHCPv6 Vendor Indetifying Vendor Class with the IANA assigned EnterpriseNumberenwith thedata.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 anddhcpcd.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 insteadof a randomly generated number.
Defining new options¶
DHCP, ND and DHCPv6 allow for the use of custom options, and RFC
3925 vendoroptions for DHCP can also be supplied.Each option needs to be
started with
thedefine
,definend
,define6
orvendopt
directive.This
can optionally be followed by
bothembed
orencap
options.Both
can be specified more than once andembed
must come
beforeencap
.
define
codetypevariable- Defines the DHCP optioncodeoftypewith a name ofvariableexported todhcpcd-run-hooks(8).
definend
codetypevariable- Defines the ND optioncodeoftypewith a name ofvariableexported todhcpcd-run-hooks(8),with a prefix ofnd_.
define6
codetypevariable- Defines the DHCPv6 optioncodeoftypewith a name ofvariableexported todhcpcd-run-hooks(8),with a prefix ofdhcp6_.
vendopt
codetypevariable- Defines the Vendor-Identifying Vendor Options.Thecodeis the IANA Enterprise Number which will uniquely describe the encapsulatedoptions.typeis normallyencap.variablenames the Vendor option to be exported.
embed
typevariable- Defines an embedded variable within the defined option.The length is determined by thetype.If thevariableis not the same as defined in the parent option,it is prefixed with the parentvariablefirst with an underscore.If thevariablehas the name ofreservedthen it is not processed.
encap
codetypevariable- Defines an encapsulated variable within the defined option.The length is determined by thetype.If thevariableis not the same as defined in the parent option,it is prefixed with the parentvariablefirst 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 userconfiguration.
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, wherethe 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 beingthe 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 generallywith 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¶
Supported Authentication Protocols¶
token
- Sends a plain text token the server expects and matches a token sent bythe server.The tokens do not have to be the same.If unspecified, the token with asecretidof 0 will be used in sending messagesand 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 fordhcpcd.conf
,writingtherealmandsecretidin it.dhcpcd
will then look for an unexpired token with a matchingrealmandsecretid.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.
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 serverwill probably have
to have its notion of the client's Replay Detection Valuereset.
monocounter
- Read the number in the file/var/lib/dhcpcd/dhcpcd-rdm.monotonicand add one to it.
monotime
- Create an NTP timestamp from the system time.
monotonic
- Same as
monotime
.
SEE ALSO¶
AUTHORS¶
Roy Marples<roy@marples.name>
BUGS¶
Please report them tohttps://roy.marples.name/projects/dhcpcd
December 18, 2023 | Debian |