.\"	$OpenBSD: hostname.if.5,v 1.82 2022/12/16 04:04:25 afresh1 Exp $
.\"	$NetBSD: hosts.5,v 1.4 1994/11/30 19:31:20 jtc Exp $
.\"
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.\"     @(#)hosts.5	8.2 (Berkeley) 12/11/93
.\"
.Dd $Mdocdate: December 16 2022 $
.Dt HOSTNAME.IF 5
.Os
.Sh NAME
.Nm hostname.if
.Nd interface-specific configuration files
.Sh DESCRIPTION
The
.Nm hostname.*\&
files contain information regarding the configuration of each network interface.
Interfaces are referenced by name and unit,
such as
.Dq hostname.fxp0 .
For some machines,
autoconfiguration makes this system inconsistent,
so interfaces can alternatively be referenced by
their link layer address (lladdr),
such as
.Dq hostname.00:00:5e:00:53:af .
Priority is given to configuration by interface lladdr over name/unit.
A configuration file is not needed for lo0.
.Pp
The configuration information is expressed in a line-by-line packed format
which makes the most common cases simpler; those dense formats are described
below.
Any lines not matching these packed formats are passed directly to
.Xr ifconfig 8 .
The packed formats are converted using a somewhat inflexible parser and
the administrator should not expect magic \(em if in doubt study
.Xr ifconfig 8
and the
per-driver manual pages to see what arguments are permitted.
.Pp
Arguments containing either whitespace or single quote
characters must be double quoted.
For example:
.Bd -literal -offset indent
inet 10.0.0.1 255.255.255.0 10.0.0.255 description "Bob's uplink"
.Ed
.Pp
Each line is processed separately and in order.
For example:
.Bd -literal -offset indent
join mynwid wpakey mywpakey
inet6 autoconf
inet autoconf
.Ed
.Pp
would run ifconfig three times to add a wireless network using WPA to the
join list and enable dynamic address configuration for IPv6 and IPv4.
.Sh STATIC ADDRESS CONFIGURATION
The following packed formats are valid for configuring network
interfaces with static addresses.
.Pp
Regular IPv4 network setup:
.Bd -ragged -offset indent
.Li inet
.Op Li alias
.Va addr
.Va netmask
.Va broadcast_addr
.Va options
.br
.Li dest
.Va dest_addr
.Ed
.Pp
Regular IPv6 network setup:
.Bd -ragged -offset indent
.Li inet6
.Op Li alias
.Va addr
.Va prefixlen
.Va options
.br
.Li dest
.Va dest_addr
.Ed
.Pp
Other network setup:
.Bd -ragged -offset indent
.Va addr_family
.Va options
.Ed
.Pp
A typical file contains only one line, but more extensive files are possible,
for example:
.Bd -literal -offset 1n
media 100baseTX description Uplink
inet 10.0.1.12 255.255.255.0 10.0.1.255
inet alias 10.0.1.13 255.255.255.255 10.0.1.13
inet alias 10.0.1.14 255.255.255.255 NONE
inet alias 10.0.1.15 255.255.255.255
inet alias 10.0.1.16 0xffffffff
# This is an example comment line.
inet6 alias fec0::1 64
inet6 alias fec0::2 64 anycast
!route add 65.65.65.65 10.0.1.13
up
.Ed
.Pp
The above formats have the following field values:
.Bl -tag -width indent -offset indent
.It Va addr_family
The address family of the interface, generally
.Dq inet
or
.Dq inet6 .
.It Li alias
The literal string
.Dq alias
if this is an additional network address for the interface.
.It Va addr
The optional address that belongs to the interface, such as
190.191.192.1 or fe80:2::1.
It is also feasible to use a hostname as specified in
.Pa /etc/hosts .
It is recommended that an address be used instead of symbolic information,
since the latter might activate resolver library routines.
.Pp
If no address is specified, the
.Va netmask ,
.Va broadcast_addr ,
.Li dest ,
and
.Va dest_addr
options are invalid and will be ignored.
.It Va netmask
The optional network mask for the interface, e.g.,
255.255.255.0.
If
.Va addr
is specified but
.Va netmask
is not, the classful mask based on
.Va addr
is used.
.It Va broadcast_addr
The optional broadcast address for the interface, e.g.,
190.191.192.255.
The word
.Dq NONE
can also be specified in order to configure the broadcast address based
on the
.Va netmask .
The
.Va netmask
option must be present in order to use this option.
.It Va options
Miscellaneous options to set on the interface, e.g.,
.Dq media 100baseTX mediaopt full-duplex .
Valid options for a particular interface type can be found in
.Xr ifconfig 8 .
When used, the
.Va netmask
and
.Va broadcast_addr
options must also be present.
.It Li dest
If the interface needs a destination address set, this is the literal text
.Dq dest .
As shown in the example, this declaration should start on a separate line.
.It Va dest_addr
The destination address to be set on the interface, such as
190.191.192.2.
It is also feasible to use a hostname as specified in
.Pa /etc/hosts .
It is recommended that an address be used instead of symbolic information
which might activate resolver library routines.
.It Va prefixlen
The prefixlen number, or number of bits in the netmask, to be set on
the interface, such as 64.
.It Li #
Comments are allowed.
Anything following a comment character is treated as a comment.
.It Li \&! Ns Ar command
Arbitrary shell commands can be executed using this directive, as
long as they are available in the single-user environment (for
instance,
.Pa /bin
or
.Pa /sbin ) .
Useful for doing interface-specific configuration such as
setting up custom routes or default source IP address using
.Xr route 8
or establishing tunnels using
.Xr ifconfig 8 .
It is worth noting that
.Dq \e$if
in a command line will be replaced by the interface name.
.Pp
For example,
to set 192.0.2.1 and 2001:db8::1 as source IP addresses for
outgoing connections:
.Bd -literal -offset indent
inet 192.0.2.1/32
inet6 2001:db8::1/128
up
!route sourceaddr -ifp \e$if
.Ed
.El
.Sh DYNAMIC ADDRESS CONFIGURATION
IPv4 dynamic addressing via DHCP is requested using
.Dq inet autoconf
followed by any options to be passed to
.Xr ifconfig 8 .
.Bd -ragged -offset indent
.Li inet autoconf
.Op Va ifconfig_options
.Ed
.Pp
The token
.Dq dhcp
on its own line without any options is short for
.Dq inet autoconf .
.Pp
IPv6 stateless address autoconfiguration is requested using
the literal string
.Dq inet6 autoconf
followed by any options to be passed to
.Xr ifconfig 8 .
.Bd -ragged -offset indent
.Li inet6 autoconf
.Op Va ifconfig_options
.Ed
.Pp
The
.Va autoconf
configurations will communicate learned DNS information to
.Xr resolvd 8 .
.Sh FILES
.Bl -tag -width "/etc/hostname.XXXXXX"
.It Pa /etc/hostname.XXX
Interface-specific configuration files.
.El
.Sh SEE ALSO
.Xr hosts 5 ,
.Xr ifconfig 8 ,
.Xr netstart 8 ,
.Xr rc 8 ,
.Xr slaacd 8