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.Dd May 24, 2024
.Dt DHCPCD.CONF 5
.Os
.Sh NAME
.Nm dhcpcd.conf
.Nd dhcpcd configuration file
.Sh DESCRIPTION
Although
.Nm 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
.Xr 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.
.Pp
Here's a list of available options:
.Bl -tag -width indent
.It Ic allowinterfaces Ar pattern
When discovering interfaces, the interface name must match
.Ar pattern
which is a space or comma separated list of patterns passed to
.Xr fnmatch 3 .
If the same interface is matched in
.Ic denyinterfaces
then it is still denied.
.It Ic denyinterfaces Ar pattern
When discovering interfaces, the interface name must not match
.Ar pattern
which is a space or comma separated list of patterns passed to
.Xr fnmatch 3 .
.It Ic 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
.Sy after
the
.Ic anonymous
option is processed.
As such, the
.Ic anonymous
option
.Sy should
be the last option in the configuration unless you really want to
send something which could identify you.
.Nm dhcpcd
will not try and reboot an old lease, it will go straight into
DISCOVER/SOLICIT.
.It Ic 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.
.It Ic arping Ar address Op address
.Nm 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:
.Pp
.D1 interface bge0
.D1 arping 192.168.0.1
.Pp
.D1 # My specific 192.168.0.1 network
.D1 profile dd:ee:aa:dd:bb:ee
.D1 static ip_address=192.168.0.10/24
.Pp
.D1 # A generic 192.168.0.1 network
.D1 profile 192.168.0.1
.D1 static ip_address=192.168.0.98/24
.It Ic authprotocol Ar protocol Op Ar algorithm Op Ar rdm
Authenticate DHCP messages.
See the Supported Authentication Protocols section.
If
.Ar protocol
is
.Ar token
then
.Ar algorithm is
snd_secretid/rcv_secretid so you can send and receive different tokens.
.It Ic authtoken Ar secretid Ar realm Ar expire Ar key
Define a shared key for use in authentication.
.Ar realm
can be "" to for use with the
.Ar delayed
protocol.
.Ar expire
is the date the token expires and should be formatted "yyy-mm-dd HH:MM".
You can use the keyword
.Ar forever
or
.Ar 0
which means the token never expires.
For the token protocol,
.Ar secretid
needs to be 0 and
.Ar realm
needs to be "".
If
.Nm dhcpcd
has the error
.D1 dhcp_auth_encode: Invalid argument
then it means that
.Nm dhcpcd
could not find the correct authentication token in your configuration.
.It Ic background
Fork to the background immediately.
This is useful for startup scripts which don't disable link messages for
carrier status.
.It Ic blacklist Ar address Ns Op /cidr
Ignores all packets from
.Ar address Ns Op /cidr .
.It Ic whitelist Ar address Ns Op /cidr
Only accept packets from
.Ar address Ns Op /cidr .
.Ic blacklist
is ignored if
.Ic whitelist
is set.
.It Ic 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.
.It Ic 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,
.Nm dhcpcd
will set this automatically.
.It Ic controlgroup Ar group
Sets the group ownership of
.Pa /run/dhcpcd/sock
so that users other than root can connect to
.Nm dhcpcd .
.It Ic debug
Echo debug messages to the stderr and syslog.
.It Ic dev Ar value
Load the
.Ar value
.Pa /dev
management module.
.Nm dhcpcd
will load the first one found to work, if any.
.It Ic env Ar value
Push
.Ar value
to the environment for use in
.Xr dhcpcd-run-hooks 8 .
For example, you can force the hostname hook to always set the hostname with
.Ic env
.Va force_hostname=YES .
Or set which driver
.Xr wpa_supplicant 8
should use with
.Ic env
.Va wpa_supplicant_driver=nl80211
.Pp
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,
.Nm dhcpcd
will still try and set a FQDN from the hostname and domain options for
consistency.
To override this, set
.Ic env
.Va hostname_fqdn=[YES|NO|SERVER] .
A value of
.Va 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.
.It Ic clientid Ar string
Send the
.Ar 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
.Ar clientid
is an empty string then
.Nm dhcpcd
sends a default
.Ar clientid
of the hardware family and the hardware address.
.It Ic duid Op 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
.Pa /var/lib/dhcpcd/duid
does not exist.
If not
.Va ll ,
.Va lt
or
.Va uuid
then
.Va value
will be converted from 00:11:22:33 format.
This, plus the IAID will be used as the
.Ic clientid .
The DUID generated will be held in
.Pa /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.
.It Ic iaid Ar iaid
Set the Interface Association Identifier to
.Ar iaid .
This option must be used in an
.Ic 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
.Nm 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.
.It Ic dhcp
Enable DHCP on the interface, on by default.
.It Ic dhcp6
Enable DHCPv6 on the interface, on by default.
.It Ic ipv4
Enable IPv4 on the interface, on by default.
.It Ic ipv6
Enable IPv6 on the interface, on by default.
.It Ic request Op Ar address
Request the
.Ar address
in the DHCP DISCOVER message.
There is no guarantee this is the address the DHCP server will actually give.
If no
.Ar address
is given then the first address currently assigned to the
.Ar interface
is used.
.It Ic inform Op Ar address Ns Op Ar /cidr Ns Op Ar /broadcast_address
Behaves like
.Ic 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
.Ar address
in use.
You should also include the optional
.Ar cidr
network number in case the address is not already configured on the interface.
.Nm dhcpcd
remains running and pretends it has an infinite lease.
.Nm dhcpcd
will not de-configure the interface when it exits.
If
.Nm dhcpcd
fails to contact a DHCP server then it returns a failure instead of falling
back on IPv4LL.
.It Ic 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
.Nm dhcpcd
is not processing IPv6 RA messages and the need for a DHCPv6 Information Request
exists.
.It Ic persistent
.Nm 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.
.It Ic fallback Ar profile
Fall back to using this profile if DHCP fails.
This allows you to configure a static profile instead of using ZeroConf.
.It Ic fallback_time Ar seconds
Start fallback after
.Ar seconds .
The default is 5 seconds.
.It Ic hostname Ar name
Sends the hostname
.Ar name
to the DHCP server so it can be registered in DNS.
If
.Ar name
is an empty string then the current system hostname is sent.
If
.Ar name
is a FQDN (i.e., contains a .) then it will be encoded as such.
.It Ic 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.
.Pp
Also, see the
.Ic env
option above to control how the hostname is set on the host.
.It Ic ia_na Op Ar iaid Op / address
Request a DHCPv6 Normal Address for
.Ar iaid .
.Ar iaid
defaults to the
.Ic iaid
option as described above.
You can request more than one ia_na by specifying a unique
.Ar iaid
for each one.
.It Ic ia_ta Op Ar iaid
Request a DHCPv6 Temporary Address for
.Ar iaid .
You can request more than one ia_ta by specifying a unique
.Ar iaid
for each one.
.It Ic ia_pd Op Ar iaid Oo / Ar prefix / Ar prefix_len Oc Op Ar interface Op / Ar sla_id Op / Ar prefix_len Op / Ar suffix
Request a DHCPv6 Delegated Prefix for
.Ar iaid .
This option must be used in an
.Ic interface
block.
Unless a
.Ar 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
.Ar interface
is given then we will assign a prefix to every other interface with a
.Ar sla_id
equivalent to the interface index assigned by the OS.
Otherwise addresses are only assigned for each
.Ar interface
and
.Ar sla_id .
To avoid delegating to any interface, use - as the invalid interface name.
Each assigned address will have a
.Ar suffix ,
defaulting to 1.
If the
.Ar suffix
is 0 then a SLAAC address is assigned.
You cannot assign a prefix to the requesting interface unless the
DHCPv6 server supports the
.Li RFC 6603
Prefix Exclude Option.
.Nm dhcpcd
has to be running for all the interfaces it is delegating to.
A default
.Ar prefix_len
of 64 is assumed, unless the maximum
.Ar sla_id
does not fit.
In this case
.Ar prefix_len
is increased to the highest multiple of 8 that can accommodate the
.Ar sla_id .
.Ar sla_id
is an integer which must be unique inside the
.Ar iaid
and is added to the prefix which must fit inside
.Ar prefix_len
less the length of the delegated prefix.
You can specify multiple
.Ar interface /
.Ar sla_id /
.Ar prefix_len
per
.Ic ia_pd ,
space separated.
IPv6RS should be disabled globally when requesting a Prefix Delegation.
.Pp
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.
.Xr 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.
.Bd -literal
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
.Ed
.It Ic ipv4only
Only configure IPv4.
.It Ic ipv6only
Only configure IPv6.
.It Ic fqdn Op disable | none | ptr | both
.Ar none
will not ask the DHCP server to update DNS.
.Ar ptr
just asks the DHCP server to update the PTR
record of the host in DNS, whereas
.Ar both
also updates the A record.
.Ar disable
will disable the FQDN option.
The default is
.Ar both .
.Nm dhcpcd
itself never does any DNS updates.
.Nm dhcpcd
encodes the FQDN hostname as specified in
.Li RFC 1035 .
.It Ic interface Ar interface
Subsequent options are only parsed for this
.Ar interface .
.It Ic ipv4ll_time Ar seconds
Wait for
.Ar seconds
before starting IPv4LL.
The default is 5 seconds.
.It Ic ipv6ra_autoconf
Generate SLAAC addresses for each Prefix advertised by an IPv6
Router Advertisement message with the Auto flag set.
On by default.
.It Ic ipv6ra_noautoconf
Disables the above option.
.It Ic ipv6ra_fork
By default, when
.Nm dhcpcd
receives an IPv6 Router Advertisement,
.Nm 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
.Nm dhcpcd
always fork on a RA.
.It Ic 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.
.It Ic leasetime Ar seconds
Request DHCP a lease time of
.Ar seconds .
.Ar -1
represents an infinite lease time.
By default
.Nm 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.
.It Ic link_rcvbuf Ar size
Override the size of the link receive buffer from the kernel default.
While
.Nm dhcpcd
will recover from link buffer overflows,
this may not be desirable on heavily loaded systems.
.It Ic logfile Ar logfile
Writes to the specified
.Ar logfile .
.Nm dhcpcd
still writes to
.Xr syslog 3 .
The
.Ar logfile
is reopened when
.Nm dhcpcd
receives the
.Dv SIGUSR2
signal.
.It Ic metric Ar metric
Metrics are used to prefer an interface over another one, lowest wins.
.Nm dhcpcd
will supply a default metric of 1000 +
.Xr if_nametoindex 3 .
This will be offset by 2000 for wireless interfaces, with additional offsets
of 1000000 for IPv4LL and 2000000 for roaming interfaces.
.It Ic mudurl Ar 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.
.It Ic noalias
Any pre-existing IPv4 addresses will be removed from the interface when
adding a new IPv4 address.
.It Ic noarp
Don't send any ARP requests.
This also disables IPv4LL.
.It Ic arp_persistdefence
Keep the IP address even if defence fails upon IP Address conflict.
.It Ic noauthrequired
Don't require authentication even though we requested it.
Also allows FORCERENEW and RECONFIGURE messages without authentication.
.It Ic nodelay
Don't delay for an initial randomised time when starting protocols.
.It Ic nodev
Don't load
.Pa /dev
management modules.
.It Ic nodhcp
Don't start DHCP or listen to DHCP messages.
This is only useful when allowing IPv4LL.
.It Ic nodhcp6
Don't start DHCPv6 or listen to DHCPv6 messages.
Normally DHCPv6 is started by an IPv6 Router Advertisement instruction or
configuration.
.It Ic nogateway
Don't install any default routes.
.It Ic gateway
Install a default route if available (default).
.It Ic nohook Ar script
Don't run this hook script.
Matches full name, or prefixed with 2 numbers optionally ending with
.Pa .sh .
.Pp
So to stop
.Nm dhcpcd
from touching your DNS settings or starting wpa_supplicant you would do:-
.D1 nohook resolv.conf, wpa_supplicant
.It Ic noipv4
Don't attempt to configure an IPv4 address.
.It Ic noipv4ll
Don't attempt to obtain an IPv4LL address if we failed to get one via DHCP.
See
.Rs
.%T "RFC 3927"
.Re
.It Ic noipv6
Don't solicit or accept IPv6 Router Advertisements and DHCPv6.
.It Ic noipv6rs
Don't solicit or accept IPv6 Router Advertisements.
.It Ic nolink
Don't receive link messages about carrier status.
You should only set this for buggy interface drivers.
.It Ic noup
Don't bring the interface up when in manager mode.
.It Ic option Ar option
Requests the
.Ar option
from the server.
It can be a variable to be used in
.Xr dhcpcd-run-hooks 8
or the numerical value.
You can specify more
.Ar option Ns s
separated by commas, spaces or more
.Ic option
lines.
Prepend dhcp6_ to
.Ar option
to request a DHCPv6 option.
If no DHCPv6 options are configured,
then DHCPv4 options are mapped to equivalent DHCPv6 options.
.Pp
Prepend nd_ to
.Ar option
to handle ND options, but this only works for the
.Ic nooption ,
.Ic reject
and
.Ic require
options.
.Pp
To see a list of options you can use, call
.Nm dhcpcd
with the
.Fl V , Fl Fl variables
argument.
.It Ic nooption Ar option
Remove the option from the message before it's processed.
.It Ic require Ar option
Requires the
.Ar option
to be present in all messages, otherwise the message is ignored.
To enforce that
.Nm dhcpcd
only responds to DHCP servers and not BOOTP servers, you can
.Ic require
.Ar dhcp_message_type .
This isn't an exact science though because a BOOTP server can send DHCP-like
options.
.It Ic reject Ar option
Reject a message that contains the
.Ar option .
This is useful when you cannot use
.Ic require
to select / de-select BOOTP messages.
.It Ic destination Ar option
If
.Nm
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.
.It Ic profile Ar name
Subsequent options are only parsed for this profile
.Ar name .
.It Ic quiet
Suppress any dhcpcd output to the console, except for errors.
.It Ic reboot Ar seconds
Allow
.Ar reboot
seconds before moving to the DISCOVER phase if we have an old lease to use.
Allow
.Ar reboot
seconds before starting fallback states from the DISCOVER phase.
IPv4LL is started when the first
.Ar reboot
timeout is reached.
The default is 5 seconds.
A setting of 0 seconds causes
.Nm
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
.Nm dhcpcd
will timeout before moving back to the DISCOVER phase.
This has no effect on DHCPv6 other than skipping the reboot phase.
.It Ic release
.Nm dhcpcd
will release the lease prior to stopping the interface.
.It Ic script Ar script
Use
.Ar script
instead of the default
.Pa /usr/lib/dhcpcd/dhcpcd-run-hooks .
.It Ic request_time Ar seconds
Request the lease for
.Ar seconds
before going back to DISCOVER.
The default is 180 seconds.
.It Ic ssid Ar ssid
Subsequent options are only parsed for this wireless
.Ar ssid .
.It Ic slaac Ic hwaddr | Ic private | Ic token Ar token Op Ic temp | Ic temporary
Selects the interface identifier used for SLAAC generated IPv6 addresses.
If
.Ic private
is used, a RFC 7217 address is generated.
If
.Ic token Ar token
is used then the token is combined with the prefix to make the final address.
The
.Ic temporary
directive will create a temporary address for the prefix as well.
.It Ic static Ar value
Configures a static
.Ar value .
If you set
.Ic ip_address
then
.Nm 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
.Ic 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
.Ic ip6_address ,
.Nm dhcpcd
will continue auto-configuration as normal.
.Pp
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
.Ic inform6
command here if you wished to obtain more information via DHCPv6.
For IPv4, you should use the
.Ic inform Ar ipaddress
option instead of setting a static address.
.D1 interface eth0
.D1 noipv6rs
.D1 static ip_address=192.168.0.10/24
.D1 static broadcast_address=192.168.0.63
.D1 static ip6_address=fd51:42f8:caae:d92e::ff/64
.D1 static routers=192.168.0.1
.D1 static domain_name_servers=192.168.0.1 fd51:42f8:caae:d92e::1
.Pp
Here is an example for PPP which gives the destination a default route.
It uses the special
.Ar destination
keyword to insert the destination address
into the value.
.D1 interface ppp0
.D1 static ip_address=0.0.0.0
.D1 destination routers
.It Ic timeout Ar seconds
Time out after
.Ar seconds ,
instead of the default 30.
A setting of 0
.Ar seconds
causes
.Nm dhcpcd
to wait forever to get a lease.
If
.Nm dhcpcd
is working on a single interface then
.Nm dhcpcd
will exit when a timeout occurs, otherwise
.Nm dhcpcd
will fork into the background.
If using IPv4LL then
.Nm dhcpcd
start the IPv4LL process after the timeout and then wait a little longer
before really timing out.
.It Ic userclass Ar string
Tag the DHCPv4 message with the userclass.
You can specify more than one.
.It Ic msuserclass Ar string
Tag the DHCPv4 mesasge with the Microsoft userclass.
Unlike the
.Ic userclass
option, this one can only be added once.
It should only be used for Microsoft DHCP servers and the
.Ic vendorclassid
should be set to "MSFT 98" or "MSFT 5.0".
This option is not RFC compliant.
.It Ic vendor Ar code , Ns Ar value
Add an encapsulated vendor option.
.Ar code
should be between 1 and 254 inclusive.
To add a raw vendor string, omit
.Ar code
but keep the comma.
Examples.
.Pp
Set the vendor option 01 with an IP address.
.D1 vendor 01,192.168.0.2
Set the vendor option 02 with a hex code.
.D1 vendor 02,01:02:03:04:05
Set the vendor option 03 with an IP address as a string.
.D1 vendor 03,\e"192.168.0.2\e"
Set un-encapsulated vendor option to hello world.
.D1 vendor ,"hello world"
.It Ic vendorclassid Ar string
Set the DHCP Vendor Class.
DHCPv6 has its own option as shown below.
The default is
dhcpcd-<version>:<os>:<machine>:<platform>.
For example
.D1 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.
.It Ic vendclass Ar en Ar data
Add the DHCPv6 Vendor Indetifying Vendor Class with the IANA assigned Enterprise
Number
.Ar en
with the
.Ar 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.
.It Ic waitip Op 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,
.Nm
will wait for any address protocol to be assigned.
It is possible to wait for more than one address protocol and
.Nm
will only fork to the background when all waiting conditions are satisfied.
.It Ic xidhwaddr
Use the last four bytes of the hardware address as the DHCP xid instead
of a randomly generated number.
.El
.Ss 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
.Ic define ,
.Ic definend ,
.Ic define6
or
.Ic vendopt
directive.
This can optionally be followed by both
.Ic embed
or
.Ic encap
options.
Both can be specified more than once and
.Ic embed
must come before
.Ic encap .
.Bl -tag -width indent
.It Ic define Ar code Ar type Ar variable
Defines the DHCP option
.Ar code
of
.Ar type
with a name of
.Ar variable
exported to
.Xr dhcpcd-run-hooks 8 .
.It Ic definend Ar code Ar type Ar variable
Defines the ND option
.Ar code
of
.Ar type
with a name of
.Ar variable
exported to
.Xr dhcpcd-run-hooks 8 ,
with a prefix of
.Va nd_ .
.It Ic define6 Ar code Ar type Ar variable
Defines the DHCPv6 option
.Ar code
of
.Ar type
with a name of
.Ar variable
exported to
.Xr dhcpcd-run-hooks 8 ,
with a prefix of
.Va dhcp6_ .
.It Ic vendopt Ar code Ar type Ar variable
Defines the Vendor-Identifying Vendor Options.
The
.Ar code
is the IANA Enterprise Number which will uniquely describe the encapsulated
options.
.Ar type
is normally
.Ar encap .
.Ar variable
names the Vendor option to be exported.
.It Ic embed Ar type Ar variable
Defines an embedded variable within the defined option.
The length is determined by the
.Ar type .
If the
.Ar variable
is not the same as defined in the parent option,
it is prefixed with the parent
.Ar variable
first with an underscore.
If the
.Ar variable
has the name of
.Ar reserved
then it is not processed.
.It Ic encap Ar code Ar type Ar variable
Defines an encapsulated variable within the defined option.
The length is determined by the
.Ar type .
If the
.Ar variable
is not the same as defined in the parent option,
it is prefixed with the parent
.Ar variable
first with an underscore.
.El
.Ss 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.
.Bl -tag -width -indent
.It Ic request
Requests the option by default without having to be specified in user
configuration.
.It Ic norequest
This option cannot be requested, regardless of user configuration.
.It Ic optional
This option is optional.
Only makes sense for embedded options like the client FQDN option, where
the FQDN string itself is optional.
.It Ic index
The option can appear more than once and will be indexed.
.It Ic array
The option data is split into a space separated array, each element being
the same type.
.El
.Ss 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.
.Bl -tag -width indent
.It Ic ipaddress
An IPv4 address, 4 bytes.
.It Ic ip6address
An IPv6 address, 16 bytes.
.It Ic string Op : Ic length
A NVT ASCII string of printable characters.
.It Ic byte
A byte.
.It Ic bitflags : Ic 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.
.It Ic int16
A signed 16bit integer, 2 bytes.
.It Ic uint16
An unsigned 16bit integer, 2 bytes.
.It Ic int32
A signed 32bit integer, 4 bytes.
.It Ic uint32
An unsigned 32bit integer, 4 bytes.
.It Ic flag
A fixed value (1) to indicate that the option is present, 0 bytes.
.It Ic domain
An RFC 3397 encoded string.
.It Ic dname
An RFC 1035 validated string.
.It Ic 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.
.It Ic binhex Op : Ic length
Binary data expressed as hexadecimal.
.It Ic embed
Contains embedded options (implies encap as well).
.It Ic encap
Contains encapsulated options (implies embed as well).
.It Ic option
References an option from the global definition.
.El
.Ss Example definition
.D1 # DHCP option 81, Fully Qualified Domain Name, RFC 4702
.D1 define 81 embed fqdn
.D1 embed byte flags
.D1 embed byte rcode1
.D1 embed byte rcode2
.D1 embed domain fqdn
.Pp
.D1 # DHCP option 125, Vendor Specific Information Option, RFC 3925
.D1 define 125 encap vsio
.D1 embed uint32 enterprise_number
.D1 # Options defined for the enterprise number
.D1 encap 1 ipaddress ipaddress
.Ss Supported Authentication Protocols
.Bl -tag -width -indent
.It Ic 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
.Ar secretid
of 0 will be used in sending messages
and validating received messages.
.It Ic delayedrealm
Delayed Authentication.
.Nm dhcpcd
will send an authentication option with no key or MAC.
The server will see this option, and select a key for
.Nm , writing the
.Ar realm
and
.Ar secretid
in it.
.Nm dhcpcd
will then look for an unexpired token with a matching
.Ar realm
and
.Ar secretid .
This token is used to authenticate all other messages.
.It Ic delayed
Same as above, but without a realm.
.El
.Ss Supported Authentication Algorithms
If none specified,
.Ic hmac-md5
is the default.
.Bl -tag -width -indent
.It Ic hmac-md5
.El
.Ss Supported Replay Detection Mechanisms
If none specified,
.Ic 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.
.Bl -tag -width -indent
.It Ic monocounter
Read the number in the file
.Pa /var/lib/dhcpcd/dhcpcd-rdm.monotonic
and add one to it.
.It Ic monotime
Create an NTP timestamp from the system time.
.It Ic monotonic
Same as
.Ic monotime .
.El
.Sh SEE ALSO
.Xr fnmatch 3 ,
.Xr if_nametoindex 3 ,
.Xr dhcpcd 8 ,
.Xr dhcpcd-run-hooks 8
.Sh AUTHORS
.An Roy Marples Aq Mt roy@marples.name
.Sh BUGS
Please report them to
.Lk https://roy.marples.name/projects/dhcpcd