IFCONFIG(8)

NAME
ifconfig - configure network interface parameters

SYNOPSIS
ifconfig interface address_family [ address [dest_address]] [parameters]
ifconfig interface [protocol_family]
ifconfig -a
ifconfig -au
ifconfig -ad

DESCRIPTION
Ifconfig is used to assign an address to a network interface and/or configure network interface parameters. Ifconfig must be used at boot time to define the network address of each interface present on a machine; it may also be used at a later time to redefine an interface's address or other operating parameters.

Available operands for ifconfig:

Address
    For the DARPA-Internet family, the address is either a host name present in the host name data base, hosts(5), or a DARPA Internet address expressed in the Internet standard “dot notation”. For the Xerox Network Systems(tm) family, addresses are net:a.b.c.d.e.f, where net is the assigned network number (in decimal), and each of the six bytes of the host number, a through f, are specified in hexadecimal. The host number may be omitted on 10Mb/s Ethernet interfaces, which use the hardware physical address, and on interfaces other than the first. For the ISO family, addresses are specified as a long hexadecimal string, as in the Xerox family. However, two consecutive dots imply a zero byte, and the dots are optional, if the user wishes to (carefully) count out long strings of digits in network byte order.

address_family
    Specifies the address family which affects interpretation of the remaining parameters. Since an interface can receive transmissions in differing protocols with different naming schemes, specifying the address family is recommended. The address or protocol families currently supported are “inet”, “iso”, and “ns”.

Interface
    The interface parameter is a string of the form “name unit”, for example, “en0”

The following parameters may be set with ifconfig:

alias
    Establish an additional network address for this interface. This is sometimes useful when changing network numbers, and one wishes to accept packets addressed to the old interface.

arp Enable the use of the Address Resolution Protocol in mapping between network level addresses and link level addresses (default). This is currently implemented for mapping between DARPA Internet addresses and 10Mb/s Ethernet addresses.

-arp
    Disable the use of the Address Resolution Protocol.

broadcast
    (Inet only) Specify the address to use to represent broadcasts to the network. The default broadcast address is the address with a host part of all 1's.

debug
    Enable driver dependent debugging code; usually, this turns on extra console error logging.

-debug
    Disable driver dependent debugging code.

delete
    Remove the network address specified. This would be used if you incorrectly specified an alias, or it was no longer needed. If you have incorrectly set an NS address having the side effect of specifying the host portion, removing all NS addresses will allow you to respecify the host portion.

dest_address
    Specify the address of the correspondent on the other end of a point to point link.

down
    Mark an interface ``down''. When an interface is marked ``down'', the system will not attempt to transmit messages through that interface. If possible, the interface will be reset to disable reception as well. This action does not automatically disable routes using the interface.

ipdst
    This is used to specify an Internet host who is willing to receive ip packets encapsulating NS packets bound for a remote network. An apparent point to point link is constructed, and the address specified will be taken as the NS address and network of the destination. IP encapsulation of CLNP packets is done differently.

metric n
    Set the routing metric of the interface to n, default 0. The routing metric is used by the routing protocol (routed(8)). Higher metrics have the effect of making a route less favorable; metrics are counted as addition hops to the destination network or host.

mtu n
    Set the maximum transmission unit of the interface to n, default is interface specific. The mtu is used to limit the size of packets that are transmitted on an interface. Not all interfaces support setting the mtu, and some interfaces have range restrictions.

netmask mask
    (Inet and ISO) Specify how much of the address to reserve for subdividing networks into sub-networks. The mask includes the network part of the local address and the subnet part, which is taken from the host field of the address. The mask can be specified as a single hexadecimal number with a leading 0x, with a dot-notation Internet address, or with a pseudo-network name listed in the network table networks(5). The mask contains 1's for the bit positions in the 32-bit address which are to be used for the network and subnet parts, and 0's for the host part. The mask should contain at least the standard network portion, and the subnet field should be contiguous with the network portion.

nsellength n
    (ISO only) This specifies a trailing number of bytes for a received NSAP used for local identification, the remaining leading part of which is taken to be the NET (Network Entity Title). The default value is 1, which is conformant to US GOSIP. When an ISO address is set in an ifconfig command, it is really the NSAP which is being specified. For example, in US GOSIP, 20 hex digits should be specified in the ISO NSAP to be assigned to the interface. There is some evidence that a number different from 1 may be useful for AFI 37 type addresses.

trailers
    Request the use of a ``trailer'' link level encapsulation when sending (default). If a network interface supports trailers, the system will, when possible, encapsulate outgoing messages in a manner which minimizes the number of memory to memory copy operations performed by the receiver. On networks that support the Address Resolution Protocol (see arp(4); currently, only 10 Mb/s Ethernet), this flag indicates that the system should request that other systems use trailers when sending to this host. Similarly, trailer encapsulations will be sent to other hosts that have made such requests. Currently used by Internet protocols only.

-trailers
    Disable the use of a ``trailer'' link level encapsulation.

link[0-2]
    Enable special processing of the link level of the interface. These three options are interface specific in actual effect, however, they are in general used to select special modes of operation. An example of this is to enable SLIP compression. Currently, only used by SLIP.

-link[0-2]
    Disable special processing at the link level with the specified interface.

up  Mark an interface ``up''. This may be used to enable an interface after an ``ifconfig down.'' It happens automatically when setting the first address on an interface. If the interface was reset when previously marked down, the hardware will be re-initialized.

Ifconfig -a displays information on all interfaces. When followed by a configuration parameter, it will also set the configuration on all interfaces.

Ifconfig -au is similar to ifconfig -a, except it only affects interfaces that are currently marked as up. Conversely, ifconfig -ad affects only interfaces that are marked down.

Ifconfig displays the current configuration for a network interface when no optional parameters are supplied. If a protocol family is specified, Ifconfig will report only the details specific to that protocol family.

Only the super-user may modify the configuration of a network interface.

DIAGNOSTICS
Messages indicating the specified interface does not exit, the requested address is unknown, or the user is not privileged and tried to alter an interface's configuration.

SEE ALSO
netstat(1), netintro(4), rc(8), routed(8),

HISTORY
The ifconfig command appeared in 4.2BSD.