hostname.* files contain information
regarding the configuration of each network interface. Interfaces are
referenced by name and unit, such as “hostname.fxp0”. For some
machines, autoconfiguration makes this system inconsistent, so interfaces
can alternatively be referenced by their link layer address (lladdr), such
as “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.
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 ifconfig(8). The packed formats are converted using a somewhat inflexible parser and the administrator should not expect magic — if in doubt study ifconfig(8) and the per-driver manual pages to see what arguments are permitted.
Arguments containing either whitespace or single quote characters must be double quoted. For example:
inet 10.0.0.1 255.255.255.0 10.0.0.255 description "Bob's uplink"
Each line is processed separately and in order. For example:
join mynwid wpakey mywpakey inet6 autoconf inet autoconf
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.
STATIC ADDRESS CONFIGURATION
The following packed formats are valid for configuring network interfaces with static addresses.
Regular IPv4 network setup:
alias] addr netmask broadcast_addr options
Regular IPv6 network setup:
alias] addr prefixlen options
Other network setup:
A typical file contains only one line, but more extensive files are possible, for example:
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 18.104.22.168 10.0.1.13 up
The above formats have the following field values:
- The address family of the interface, generally “inet” or “inet6”.
- The literal string “alias” if this is an additional network address for the interface.
- The optional address that belongs to the interface, such as 22.214.171.124
or fe80:2::1. It is also feasible to use a hostname as specified in
/etc/hosts. It is recommended that an address be
used instead of symbolic information, since the latter might activate
resolver library routines.
If no address is specified, the netmask, broadcast_addr,
dest, and dest_addr options are invalid and will be ignored.
- The optional network mask for the interface, e.g., 255.255.255.0. If addr is specified but netmask is not, the classful mask based on addr is used.
- The optional broadcast address for the interface, e.g., 126.96.36.199. The word “NONE” can also be specified in order to configure the broadcast address based on the netmask. The netmask option must be present in order to use this option.
- Miscellaneous options to set on the interface, e.g., “media 100baseTX mediaopt full-duplex”. Valid options for a particular interface type can be found in ifconfig(8). When used, the netmask and broadcast_addr options must also be present.
- If the interface needs a destination address set, this is the literal text “dest”. As shown in the example, this declaration should start on a separate line.
- The destination address to be set on the interface, such as 188.8.131.52. It is also feasible to use a hostname as specified in /etc/hosts. It is recommended that an address be used instead of symbolic information which might activate resolver library routines.
- The prefixlen number, or number of bits in the netmask, to be set on the interface, such as 64.
- Comments are allowed. Anything following a comment character is treated as a comment.
- Arbitrary shell commands can be executed using this directive, as long as
they are available in the single-user environment (for instance,
/bin or /sbin). Useful for
doing interface-specific configuration such as setting up custom routes or
default source IP address using
or establishing tunnels using
ifconfig(8). It is worth noting that “\$if” in a
command line will be replaced by the interface name.
For example, to set 192.0.2.1 and 2001:db8::1 as source IP addresses for outgoing connections:
inet 192.0.2.1/32 inet6 2001:db8::1/128 up !route sourceaddr -ifp \$if
DYNAMIC ADDRESS CONFIGURATION
IPv4 dynamic addressing via DHCP is requested using “inet autoconf” followed by any options to be passed to ifconfig(8).
The token “dhcp” on its own line without any options is short for “inet autoconf”.
IPv6 stateless address autoconfiguration is requested using the literal string “inet6 autoconf” followed by any options to be passed to ifconfig(8).
The autoconf configurations will communicate learned DNS information to resolvd(8).
- Interface-specific configuration files.
hosts(5), ifconfig(8), netstart(8), rc(8), slaacd(8)