github.com/niedbalski/juju@v0.0.0-20190215020005-8ff100488e47/network/debinterfaces/testdata/ifupdown-examples

# This is a copy of the example interfaces file from the ifupdown
# package.

######################################################################
# /etc/network/interfaces -- configuration file for ifup(8), ifdown(8)
#
# A "#" character in the very first column makes the rest of the line
# be ignored. Blank lines are ignored. Lines may be indented freely.
# A "\" character at the very end of the line indicates the next line
# should be treated as a continuation of the current one.
#
# The "pre-up", "up", "down" and "post-down" options are valid for all 
# interfaces, and may be specified multiple times. All other options
# may only be specified once.
#
# See the interfaces(5) manpage for information on what options are 
# available.
######################################################################

# The loopback interface isn't really required any longer,
# but can be used if needed.
#
auto lo
iface lo inet loopback

# An example ethernet card setup: (broadcast and gateway are optional)
#
auto eth0
iface eth0 inet static
    address 192.168.0.42/24
    gateway 192.168.0.1

# A more complicated ethernet setup, with a less common netmask, and a downright
# weird broadcast address: (the "up" lines are executed verbatim when the 
# interface is brought up, the "down" lines when it's brought down)
#
auto eth0
iface eth0 inet static
    address 192.168.1.42/25
    up route add -net 192.168.1.128 netmask 255.255.255.128 gw 192.168.1.2
    up route add default gw 192.168.1.200
    down route del default gw 192.168.1.200
    down route del -net 192.168.1.128 netmask 255.255.255.128 gw 192.168.1.2

# A more complicated ethernet setup with a single ethernet card with
# two interfaces.
# Note: This happens to work since ifconfig handles it that way, not because
# ifup/down handles the ':' any differently.
# Warning: There is a known bug if you do this, since the state will not
# be properly defined if you try to 'ifdown eth0' when both interfaces
# are up. The ifconfig program will not remove eth0 but it will be
# removed from the interfaces state so you will see it up until you execute:
# 'ifdown eth0:1 ; ifup eth0; ifdown eth0'
# BTW, this is "bug" #193679 (it's not really a bug, it's more of a 
# limitation)
#
auto eth0 eth0:1
iface eth0 inet static
    address 192.168.0.100/24
    gateway 192.168.0.1
iface eth0:1 inet static
    address 192.168.0.200
    netmask 255.255.255.0

# Another way to accomplish this:
#
auto eth0
iface eth0 inet static
    address 192.168.0.100/24
    gateway 192.168.0.1
iface eth0 inet static
    address 192.168.0.200
    netmask 255.255.255.0
#
# However, when specifying multiple addresses this way, there will be no
# way to add or remove them individually using ifup/ifdown only.

# "pre-up" and "post-down" commands are also available. In addition, the
# exit status of these commands are checked, and if any fail, configuration
# (or deconfiguration) is aborted. So:
#
auto eth0
iface eth0 inet dhcp
    pre-up [ -f /etc/network/local-network-ok ]
#
# will allow you to only have eth0 brought up when the file 
# /etc/network/local-network-ok exists.

# Two ethernet interfaces, one connected to a trusted LAN, the other to
# the untrusted Internet. If their MAC addresses get swapped (because an
# updated kernel uses a different order when probing for network cards,
# say), then they don't get brought up at all.
#
auto eth0 eth1
iface eth0 inet static
    address 192.168.42.1
    netmask 255.255.255.0
    pre-up /path/to/check-mac-address.sh eth0 11:22:33:44:55:66
    pre-up /usr/local/sbin/enable-masq
iface eth1 inet dhcp
    pre-up /path/to/check-mac-address.sh eth1 AA:BB:CC:DD:EE:FF
    pre-up /usr/local/sbin/firewall

# Two ethernet interfaces, one connected to a trusted LAN, the other to
# the untrusted Internet, identified by MAC address rather than interface
# name:
#
auto eth0 eth1
mapping eth0 eth1
    script /path/to/get-mac-address.sh
    map 11:22:33:44:55:66 lan
    map AA:BB:CC:DD:EE:FF internet
iface lan inet static
    address 192.168.42.1
    netmask 255.255.255.0
    pre-up /usr/local/sbin/enable-masq $IFACE
iface internet inet dhcp
    pre-up /usr/local/sbin/firewall $IFACE

# A PCMCIA interface for a laptop that is used in different locations:
# (note the lack of an "auto" line for any of these)
#
mapping eth0
   script /path/to/pcmcia-compat.sh
   map home,*,*,*                  home
   map work,*,*,00:11:22:33:44:55  work-wireless
   map work,*,*,01:12:23:34:45:50  work-static
#
iface home inet dhcp
iface work-wireless bootp
iface work-static static
    address 10.15.43.23
    netmask 255.255.255.0
    gateway 10.15.43.1
#
# Note, this won't work unless you specifically change the file
# /etc/pcmcia/network to look more like:
#
#     if [ -r ./shared ] ; then . ./shared ; else . /etc/pcmcia/shared ; fi
#     get_info $DEVICE
#     case "$ACTION" in
#         'start')
#             /sbin/ifup $DEVICE
#             ;;
#         'stop')
#             /sbin/ifdown $DEVICE
#             ;;
#     esac
#     exit 0

# An alternate way of doing the same thing: (in this case identifying
# where the laptop is is done by configuring the interface as various
# options, and seeing if a computer that is known to be on each particular
# network will respond to pings. The various numbers here need to be chosen
# with a great deal of care.)
#
mapping eth0
   script /path/to/ping-places.sh
   map 192.168.42.254/24 192.168.42.1 home
   map 10.15.43.254/24 10.15.43.1 work-wireless
   map 10.15.43.23/24 10.15.43.1 work-static
#
iface home inet dhcp
iface work-wireless bootp
iface work-static static
    address 10.15.43.23
    netmask 255.255.255.0
    gateway 10.15.43.1
#
# Note that the ping-places script requires the iproute package installed,
# and the same changes to /etc/pcmcia/network are required for this as for
# the previous example.


# Set up an interface to read all the traffic on the network. This 
# configuration can be useful to setup Network Intrusion Detection
# sensors in 'stealth'-type configuration. This prevents the NIDS
# system to be a direct target in a hostile network since they have
# no IP address on the network. Notice, however, that there have been
# known bugs over time in sensors part of NIDS (for example see 
# DSA-297 related to Snort) and remote buffer overflows might even be
# triggered by network packet processing.
# 
auto eth0
iface eth0 inet manual
	up ifconfig $IFACE 0.0.0.0 up
	up ip link set $IFACE promisc on
	down ip link set $IFACE promisc off
	down ifconfig $IFACE down

# Set up an interface which will not be allocated an IP address by
# ifupdown but will be configured through external programs. This
# can be useful to setup interfaces configured through other programs,
# like, for example, PPPOE scripts.
#
auto eth0
iface eth0 inet manual
      up ifconfig $IFACE 0.0.0.0 up
      up /usr/local/bin/myconfigscript
      down ifconfig $IFACE down