/etc/network/interfaces
Stephen R Laniel
steve at laniels.org
Sat Sep 17 15:25:56 UTC 2005
On Sat, Sep 17, 2005 at 11:11:44AM -0400, Adam Maddock wrote:
> I'm new to Ubuntu, but not to Linux (most experience with Slackware). Does
> anybody have a reference to the syntax for the network interfaces file (path in
> subject). I'm building a firewall machine and need to add another Interface.
> I could easily cluge it with some ifconfig commands, but I'd like to do it the
> proper way for this distro.
See the man page for interfaces(5). I include it below.
INTERFACES(5) File formats INTERFACES(5)
NAME
/etc/network/interfaces - network interface configuration for ifup and
ifdown
DESCRIPTION
/etc/network/interfaces contains network interface configuration infor
mation for the ifup(8) and ifdown(8) commands. This is where you con
figure how your system is connected to the network.
Lines starting with # are ignored. Note that end-of-line comments are
NOT supported, comments must be on a line of their own.
A line may be extended across multiple lines by making the last charac
ter a backslash.
The file consists of zero or more "iface", "mapping", "auto" and
"allow-" stanzas. Here is an example.
auto lo eth0
allow-hotplug eth1
iface lo inet loopback
mapping eth0
script /usr/local/sbin/map-scheme
map HOME eth0-home
map WORK eth0-work
iface eth0-home inet static
address 192.168.1.1
netmask 255.255.255.0
up flush-mail
iface eth0-work inet dhcp
iface eth1 inet dhcp
Lines beginning with the word "auto" are used to identify the physical
interfaces to be brought up when ifup is run with the -a option. (This
option is used by the system boot scripts.) Physical interface names
should follow the word "auto" on the same line. There can be multiple
"auto" stanzas. ifup brings the named interfaces up in the order
listed.
Lines beginning with "allow-" are used to identify interfaces that
should be brought up automatically by various subsytems. This may be
done using a command such as "ifup --allow=hotplug eth0 eth1", which
will only bring up eth0 or eth1 if it is listed in an "allow-hotplug"
line. Note that "allow-auto" and "auto" are synonyms.
Stanzas beginning with the word "mapping" are used to determine how a
logical interface name is chosen for a physical interface that is to be
brought up. The first line of a mapping stanza consists of the word
"mapping" followed by a pattern in shell glob syntax. Each mapping
stanza must contain a script definition. The named script is run with
the physical interface name as its argument and with the contents of
all following "map" lines (without the leading "map") in the stanza
provided to it on its standard input. The script must print a string on
its standard output before exiting. See /usr/share/doc/ifupdown/exam
ples for examples of what the script must print.
Mapping a name consists of searching the remaining mapping patterns and
running the script corresponding to the first match; the script outputs
the name to which the original is mapped.
ifup is normally given a physical interface name as its first
non-option argument. ifup also uses this name as the initial logical
name for the interface unless it is accompanied by a suffix of the
form =LOGICAL, in which case ifup chooses LOGICAL as the initial logi
cal name for the interface. It then maps this name, possibly more than
once according to successive mapping specifications, until no further
mappings are possible. If the resulting name is the name of some
defined logical interface then ifup attempts to bring up the physical
interface as that logical interface. Otherwise ifup exits with an
error.
Stanzas defining logical interfaces start with a line consisting of the
word "iface" followed by the name of the logical interface. In simple
configurations without mapping stanzas this name should simply be the
name of the physical interface to which it is to be applied. (The
default mapping script is, in effect, the echo command.) The interface
name is followed by the name of the address family that the interface
uses. This will be "inet" for TCP/IP networking, but there is also
some support for IPX networking ("ipx"), and IPv6 networking ("inet6").
Following that is the name of the method used to configure the inter
face.
Additional options can be given on subsequent lines in the stanza.
Which options are available depends on the family and method, as
described below. Additional options can be made available by other
Debian packages. For example, the wireless-tools package makes avail
able a number of options prefixed with "wireless-" which can be used to
configure the interface using iwconfig(8). (See wireless(7) for
details.)
Options are usually indented for clarity (as in the example above) but
are not required to be.
IFACE OPTIONS
The following "command" options are available for every family and
method. Each of these options can be given multiple times in a single
stanza, in which case the commands are executed in the order in which
they appear in the stanza. (You can ensure a command never fails by
suffixing "|| true".)
pre-up command
Run command before bringing the interface up. If this command
fails then ifup aborts, refraining from marking the interface as
configured, prints an error message, and exits with status 0.
This behavior may change in the future.
up command
post-up command
Run command after bringing the interface up. If this command
fails then ifup aborts, refraining from marking the interface as
configured (even though it has really been configured), prints
an error message, and exits with status 0. This behavior may
change in the future.
down command
pre-down command
Run command before taking the interface down. If this command
fails then ifdown aborts, marks the interface as deconfigured
(even though it has not really been deconfigured), and exits
with status 0. This behavior may change in the future.
post-down command
Run command after taking the interface down. If this command
fails then ifdown aborts, marks the interface as deconfigured,
and exits with status 0. This behavior may change in the
future.
There exists for each of the above mentioned options a directory
/etc/network/if-<option>.d/ the scripts in which are run (with no argu
ments) using run-parts(8) after the option itself has been processed.
All of these commands have access to the following environment vari
ables.
IFACE physical name of the interface being processed
LOGICAL
logical name of the interface being processed
ADDRFAM
address family of the interface
METHOD method of the interface (e.g., static)
MODE start if run from ifup, stop if run from ifdown
PHASE as per MODE, but with finer granularity, distinguishing the pre-
up, post-up, pre-down and post-down phases.
VERBOSITY
indicates whether --verbose was used; set to 1 if so, 0 if not.
PATH the command search path: /usr/local/sbin:/usr/local/bin:
/usr/sbin:/usr/bin:/sbin:/bin
Additionally, all options given in an interface definition stanza are
exported to the environment in upper case with "IF_" prepended and with
hyphens converted to underscores and non-alphanumeric characters dis
carded.
INET ADDRESS FAMILY
This section documents the methods available in the inet address fam
ily.
The loopback Method
This method may be used to define the IPv4 loopback interface.
Options
(No options)
The static Method
This method may be used to define ethernet interfaces with statically
allocated IPv4 addresses.
Options
address address
Address (dotted quad) required
netmask netmask
Netmask (dotted quad) required
broadcast broadcast_address
Broadcast address (dotted quad)
network network_address
Network address (dotted quad) required for 2.0.x kernels
metric metric
Routing metric for default gateway (integer)
gateway address
Default gateway (dotted quad)
pointopoint address
Address of other end point (dotted quad). Note the
spelling of "point-to".
media type
Medium type, driver dependent
hwaddress class address
Hardware Address. class is one of ether, ax25, ARCnet or
netrom. address is dependent on the above choice.
mtu size
MTU size
The manual Method
This method may be used to define interfaces for which no configuration
is done by default. Such interfaces can be configured manually by means
of up and down commands or /etc/network/if-*.d scripts.
Options
(No options)
The dhcp Method
This method may be used to obtain an address via DHCP with any of the
tools: dhclient, pump, udhcpc, dhcpcd. (They have been listed in their
order of precedence.) If you have a complicated DHCP setup you should
note that some of these clients use their own configuration files and
do not obtain their configuration information via ifup.
Options
hostname hostname
Hostname to be requested (pump, dhcpcd, udhcpc)
leasehours leastime
Preferred lease time in hours (pump)
leasetime leasetime
Preferred lease time in seconds (dhcpcd)
vendor vendor
Vendor class identifier (dhcpcd)
client client_id
Client identifier (dhcpcd, udhcpc)
hwaddress class address
Hardware Address. class is one of ether, ax25, ARCnet or
netrom. address is dependent on this choice.
The bootp Method
This method may be used to obtain an address via bootp.
Options
bootfile file
Tell the server to use file as the bootfile.
server address
Use the IP address address to communicate with the
server.
hwaddr addr
Use addr as the hardware address instead of whatever it
really is.
The ppp Method
This method uses pon/poff to configure a PPP interface. See those com
mands for details.
Options
provider name
Use name as the provider (from /etc/ppp/peers).
The wvdial Method
This method uses wvdial to configure a PPP interface. See that command
for more details.
Options
provider name
Use name as the provider (from /etc/ppp/peers).
IPX ADDRESS FAMILY
This section documents the methods available in the ipx address family.
The static Method
This method may be used to setup an IPX interface. It requires the
ipx_interface command.
Options
frame type
type of ethernet frames to use (e.g. 802.2)
netnum id
Network number
The dynamic Method
This method may be used to setup an IPX interface dynamically.
Options
frame type
type of ethernet frames to use (e.g. 802.2)
INET6 ADDRESS FAMILY
This section documents the methods available in the inet6 address fam
ily.
The loopback Method
This method may be used to define the IPv6 loopback interface.
Options
(No options)
The static Method
This method may be used to define interfaces with statically assigned
IPv6 addresses.
Options
address address
Address (colon delimited) required
netmask mask
Netmask (number of bits, eg 64) required
gateway address
Default gateway (colon delimited)
media type
Medium type, driver dependent
hwaddress class address
Hardware Address. class is one of ether, ax25, ARCnet or
netrom. address is dependent on this choice.
mtu size
MTU size
The v4tunnel Method
This method may be used to setup an IPv6-over-IPv4 tunnel. It requires
the ip command from the iproute package.
Options
address address
Address (colon delimited)
netmask mask
Netmask (number of bits, eg 64)
endpoint address
Address of other tunnel endpoint (IPv4 dotted quad)
required
local address
Address of the local endpoint (IPv4 dotted quad)
gateway address
Default gateway (colon delimited)
ttl time
TTL setting
KNOWN BUGS/LIMITATIONS
The ifup and ifdown programs work with so-called "physical" interface
names. These names are assigned to hardware by the kernel. Unfortu
nately it can happen that the kernel assigns different physical inter
face names to the same hardware at different times; for example, what
was called "eth0" last time you booted is now called "eth1" and vice
versa. This creates a problem if you want to configure the interfaces
appropriately. A way to deal with this problem is to use mapping
scripts that choose logical interface names according to the properties
of the interface hardware. See the get-mac-address.sh script in the
examples directory for an example of such a mapping script. See also
Debian bug #101728.
It is not currently possible to divide up /etc/network/interfaces into
multiple files. A feature that would make this possible is some sort
of inclusion directive. No such feature exists in the current ifupdown
program. For more information see Debian bug #159884.
AUTHOR
The ifupdown suite was written by Anthony Towns <aj at azure.hum
bug.org.au>. This manpage was contributed by Joey Hess
<joey at kitenet.net>.
SEE ALSO
ifup(8), iwconfig(8), run-parts(8).
For advice on configuring this package read the Network Configuration
chapter of the Debian Reference manual, available at
http://www.debian.org/doc/manuals/reference/ch-gateway.en.html or in
the debian-reference-en package.
Examples of how to set up interfaces can be found in
/usr/share/doc/ifupdown/examples/network-interfaces.
ifupdown 5 April 2004 INTERFACES(5)
--
Stephen R. Laniel
steve at laniels.org
+(617) 308-5571
http://laniels.org/
PGP key: http://laniels.org/slaniel.key
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