.Dd January 16, 2023
.Dt DHCLIENT.CONF 5
.Os
.Sh NAME
.Nm dhclient.conf
.Nd dhcp client configuration
.Sh SYNOPSIS
.Nm /etc/dhclient.${mac}.conf
.Nm /etc/dhclient.${if}.conf
.Nm /etc/dhclient.conf
.Sh DESCRIPTION
.Xr dhclient 8
configures the network interface according to its
.Nm
configuration file, searching for the first file path to exist:
.Pp
.Bl -bullet -compact
.It
.Pa /etc/dhclient.${mac}.conf
- where
.Ar mac
is the network interface's hardware address.
(Example:
.Pa dhclient.00:00:5e:00:53:00.conf )
.It
.Pa /etc/dhclient.${if}.conf
- where
.Ar if
is the network interface's name.
(Example:
.Pa dhclient.if0.conf )
.It
.Pa /etc/dhclient.conf
- the shared configuration file.
.El
.Pp
Network interface names are not guaranteed to be stable and it's recommended to
use the hardware address in the file name or in the
.Sy if
statement in the shared file.
.Sh FORMAT
.Nm
contains a series of whitespace delimited tokens akin to an
.Xr ifconfig 8
invocation.
The
.Sq #
character begins a comment and the rest of the line is ignored.
If a token names a protocol, then that protocol is selected.
If a token names a configuration inside the current protocol or a top level
statement, then that configuration is set to the value of the subsequent
token.
.Pp
Configurations can be generally be set to either a manual value, or
.Sy auto
to obtain the value from the DHCP server, or
.Sy none
to disable setting the configuration and retain the currently set value.
If
.Sy auto
or
.Sy none
follows a protocol name, then all the configurations inside the protocol is set
to that value.
.Pp
The top level statements are:
.Bl -tag -width "12345678"
.It Sy if Oo Ar name "|" Sy etherhw: Ns Ar mac "|" Sy id: Ns Ar linkid Oc
The following configurations only applies to the network interface if it
matches by its
.Ar name ,
its hardware address
.Ar mac ,
or its unstable index number
.Ar linkid .
The
.Sy if
statement can only be used in the shared
.Pa /etc/dhclient.conf
file and allows defining a section for each network interface.
Configurations are applied to all network interfaces until the
.Sy if
statement appears.
.El
.Pp
The
.Sy inet
protocol contains the following configurations:
.Bl -tag -width "12345678"
.It Sy address Oo Ar ip "|" Sy auto "|" Sy none Oc
The local address in
.Xr inet 4
address notation.
(Default:
.Sy auto )
.It Sy router Oo Ar ip "|" Sy auto "|" Sy none Oc
The default route in
.Xr inet 4
address notation.
(Default:
.Sy auto )
.It Sy subnet Oo Ar ip "|" Sy auto "|" Sy none Oc
The subnet mask in
.Xr inet 4
address notation.
(Default:
.Sy auto )
.El
.Pp
The
.Sy dns
protocol contains the following configurations:
.Bl -tag -width "12345678"
.It Sy servers Oo Ar ip1,ip2,... "|" Sy auto "|" Sy none Oc
The comma separated list of DNS servers in
.Xr inet 4
address notation.
A singular comma means the empty list.
(Default:
.Sy auto )
.El
.Pp
The
.Sy ether
protocol contains the following configurations:
.Bl -tag -width "12345678"
.It Sy address Oo Ar mac "|" Sy auto "|" Sy none Oc
The local address in
.Xr ether 4
address notation.
.Sy auto
sets it to the hardware address.
(Default:
.Sy auto )
.El
.Sh EXAMPLES
.Ss Manually configuring an interface
To fully manually configure the network interface
.Pa if0 ,
even if the network interface's device name changes over time, first first look
up its ethernet hardware address:
.Bd -literal -offset indent
$ ifconfig -l if0 ether hwaddress
00:00:5e:00:53:00
.Ed
.Pp
Then write an
.Pa /etc/dhclient.conf
section using the
.Sy if
statement:
.Bd -literal -offset indent
if etherhw:00:00:5e:00:53:00
inet address 192.0.2.4 router 192.0.2.1 subnet 255.255.255.0
dns servers 192.0.2.2 192.0.2.3
.Ed
.Ss Obtaining the DNS servers on only one interface
The DNS server list is global and a system with multiple network interfaces can
obtain the list on only the preferred interface by disabling DNS configuration
and enabling it on the desired interface:
.Bd -literal -offset indent
dns none
if etherhw:00:00:5e:00:53:00
dns auto
.Ed
.Ss Disabling dhclient
.Xr dhclient 8
can be disabled on an interface by disabling configuration of the inet and dns
protocols:
.Bd -literal -offset indent
inet none
dns none
.Ed
.Sh SEE ALSO
.Xr ether 4 ,
.Xr if 4 ,
.Xr inet 4 ,
.Xr dhclient 8 ,
.Xr dnsconfig 8 ,
.Xr ifconfig 8
.Sh CAVEATS
The list of DNS servers is global and should only be obtained on one network
interface to avoid interference.