Ifconfig is used to set up (and maintain thereafter) the kernel-resident network interfaces. It is used at boot
time to configure most of them to a running state. After that, it is usually only needed when debugging or when
system tuning is needed.
If no arguments are given, ifconfig just displays the status of the currently defined interfaces. If the
single interface argument is given, it displays the status of the given interface only. Otherwise, it assumes
that things have to be set up.
If the first argument after the interface name is recog nized as the name of a supported address family, that address
family is used for decoding and displaying all protocol addresses. Currently supported address families include
inet (TCP/IP, default) and ax25 (AMPR Packet Radio.)
interface - The name of the NET interface. This usually is a name like wd0, sl3 or something
like that: a device driver name followed by a unit number.
up - This flag causes the interface to be activated. It is implicitly specified if the interface is given
a new address (see below). down - This flag causes the driver for this interface to be shut down, and is useful when things start going
wrong. [-]arp - Enable or disable the use of the ARP protocol on this interface. If the minus (-)sign is present,
the flag is turned OFF.
[-]trailers - Enable or disable the use of trailers on Ethernet frames. This is not used in the current
implementation of NET. [-]allmulti - Enable or disable the ppo i is sc cu uo ou us s mode of the interface. This means that all
incoming frames get sent to the network layer of the system kernel, allowing for networking monitoring.
m me et tr ri ic c N N This parameter sets the interface metric. It is not used at present, but we implement it
for the future.
m mt tu u N N This parameter sets the Maximum Transfer Unit (MTU) of an interface. For Ethernet, this is a number
in the range of 1000-2000 (default is 1500). For SLIP, use something between 200 and 4096. Note, that the current
implementation does not handle IP fragmentation yet, so you'd better make the MTU large enough!
d ds st ta ad dd dr r a ad dd dr r Set the "other end"'s IP address in case of a Point-To-Point link,
like PPP. This keywords is obsoleted by the new p po oi in nt to op po oi in nt t keyword.
n ne et tm ma as sk k a ad dd dr r Set the IP network mask for this interface. This value defaults to the usual
class A, B or C network mask (as deducted from the interface IP address), but it can be set to any value for the
use of sub- netting.
[ [- -] ]b br ro oa ad dc ca as st t [ [a ad dd dr r] ] If the address argument is also given, set the pro- tocol
broadcast address for this interface. Other- wise, it only sets the I IF FF F_ _B BR RO OA AD DC CA AS ST T flag
of the interface. If the keyword was preceded by a minus ( (- -) ) sign, then the flag is cleared instead.
[ [- -] ]p po oi in nt to op po oi in nt t [ [a ad dd dr r] ] This keyword enables the p po oi in nt t- -t to o-
-p po oi in nt t mode of an interface, meaning that it is a direct link between two machines with nobody else listening
on it (or, at least we hope that this is the case, grin :-) If the address argument is also given, set the pro-
tocol address of the other side of the link, just like the obsolete d ds st ta ad dd dr r keyword does. Otherwise,
it only sets the I IF FF F_ _P PO OI IN NT TO OP PO OI IN NT T flag of the inter- face. If the keyword was preceded
by a minus ( (- -) ) sign, then the flag is cleared instead.
h hw w Set the hardware address of this interface, if the device driver supports this operation. The keyword must
be followed by the name of the hardware class and the printable ASCII equivalent of the hardware address. Hardware
classes currently supported include e et th he er r (Ethernet), a ax x2 25 5 (AMPR AX.25), and A AR RC Cn ne et
a ad dd dr re es ss s The host name or IP address (a host name will be resolved into an IP address) of that interface.
This parameter is required, although the syntax doesn't currently require it.
F FI IL LE ES S _ /_ p_ r_ o_ c_ /_ n_ e_ t_ /_ s_ o_ c_ k_ e_ t _ /_ p_ r_ o_ c_ /_ n_ e_ t_ /_ d_ e_ v
B BU UG GS S None so far, although the syntax checking could be better.
A AU UT TH HO OR R Fred N. van Kempen,