HOSTNAME.IF(5) | File Formats Manual | HOSTNAME.IF(5)

# NAME

`hostname.if` — interface-specific configuration files

# DESCRIPTION

The `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:

`inet` [`alias`] addr netmask broadcast_addr options
`dest` dest_addr

Regular IPv6 network setup:

`inet6` [`alias`] addr prefixlen options
`dest` dest_addr

Other network setup:

addr_family options

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 65.65.65.65 10.0.1.13
    up

The above formats have the following field values:

addr_family
  The address family of the interface, generally “inet” or “inet6”.
`alias`
  The literal string “alias” if this is an additional network address for the interface.
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 /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.

netmask
  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.
broadcast_addr
  The optional broadcast address for the interface, e.g., 190.191.192.255. 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.
options
  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.
`dest`
  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.
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 /etc/hosts. It is recommended that an address be used instead of symbolic information which might activate resolver library routines.
prefixlen
  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.
`!`command
  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 route(8) 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).

`inet autoconf` [ifconfig_options]

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).

`inet6 autoconf` [ifconfig_options]

The autoconf configurations will communicate learned DNS information to resolvd(8).

# FILES

/etc/hostname.XXX
  Interface-specific configuration files.

# SEE ALSO

hosts(5), ifconfig(8), netstart(8), rc(8), slaacd(8)

December 16, 2022 | Debian