configure network interface parameters
ifconfig interface [ -p ]
[ address_family ]
[ address [ remote_address ] ]
[ command ... ]
ifconfig assigns an address to a network
interface and/or configures 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 operational parameters.
The interface argument is a string catenated from
the name of the network driver and its unit number (n).
These are some examples:
An interface may receive transmissions in differing
protocols, each of which may require separate naming
schemes. The address_family provides for specifying
a family of protocols, and this specification may change the
interpretation of the remaining arguments. Currently only inet
for Version 4 of the Internet Protocol family is supported. This is the
For the Internet Protocol family, the address is
either a host name present in the
or an Internet address expressed in
The remote_address need only be specified to identify
the address of the correspondent on the other end
of a SLIP or PPP link.
Displays information about all
Execute slink to link the specified interface into the TCP/IP stack.
This will only be done if the interface is not already linked when
ifconfig tries to set the interface address.
This option is only used when TCP is started.
It is required for a small number of network adapters
to which an interface cannot be linked until TCP/IP is
running and available to download microcode to the adapter
when the driver is opened.
ifconfig understands the following commands:
Establish an additional network address for this interface.
This is useful when packets need to be received that are
addressed to a defunct network address, or for
creating virtual domains on a host.
Remove the specified alias.
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 Internet addresses and
Ethernet addresses. This option is not applicable
in the STREAMS environment. Use of arp
for an interface is specified in the /etc/strcf file.
The arp driver will be opened when the
STREAMS stack is built.
Disable the use of the Address Resolution Protocol.
(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.
Enable packet logging of IP datagrams on PPP interfaces
(ppp0, ppp1, and so on).
If n is set to 1, logging is enabled. If set to 0, logging is
disabled (the default). When enabled, the IP protocol support
module will decode IP datagrams containing UDP
datagrams or TCP segments and write this information
to the PPP log file (usually /var/adm/log/ppp.log).
Enable driver dependent debugging code; usually, this turns on
extra console error logging.
n specifies the debugging level.
A level of 0 turns off debugging.
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 and
it does not break (hang up) the physical connection for SLIP and
Enable the first link-specific parameter.
Disable the first link-specific parameter.
Enable the second link-specific parameter.
Disable the second link-specific parameter.
Enable the third link-specific parameter.
Disable the third link-specific parameter.
Set the routing metric of the interface to n,
The routing metric is used by the routing daemon
Higher metrics have the effect of making a route less
favorable; metrics are counted as additional hops to the
destination network or host.
Set the Maximum Transfer Unit (MTU) size of the interface to
This should not normally be done except for debugging purposes.
Note that no validity checking is performed on the
specified MTU value; this
means that the unwary administrator can raise
the MTU of an interface
to a value larger than allowed by the hardware.
(inet only) 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
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.
onepacket size count
Enable the one-packet mode of operation (used for
interfaces that cannot handle back-to-back packets). The
keyword onepacket must be followed by two numeric
parameters: size specifies the small packet size in bytes and
count specifies the small packet threshold.
If small packet detection is not desired,
these values should be zero. See
for an explanation of one-packet mode.
Disable one-packet mode.
perf recv_size send_size use_fullsize
Tune interface-specific performance parameters.
must be followed by three numeric parameters:
Specifies the size in bytes of the TCP receive window.
Specifies the size in bytes of the TCP send window.
If set to 0,
TCP will truncate the size of each segment
to a multiple of 1KB that will fit in a frame.
If set to 1, TCP will
will use all available space in a frame for each segment.
If TCP large window scaling is enabled
(see rfc1323), the maximum possible
value of recv_size and send_size is
1073725440 ((2^16-1)2^14) bytes.
If TCP large window scaling is disabled
the maximum value is 65535 (2^16-1) bytes.
Turn on TCP large window scaling and timestamps
(see RFC 1323) for an interface.
Large window scaling is recommended for long fat networks (LFNs)
which have a capacity (defined as the bandwidth of the network
in bytes per second times the round-trip delay in seconds)
that is greater than 65,535 bytes. The sizes of the TCP
receive and send windows (configured using the perf command)
should be set equal to the capacity up to a maximum value of
1,073,725,440 ((2^16-1)2^14) bytes.
Timestamps protect against wrapped sequence numbers when the time
taken to transmit 2^32 (4,294,967,296)
bytes of data on a network is less than
the value of the maximum segment lifetime (MSL).
Timestamps should be enabled if the product of the
bandwidth of the network in bytes per second multiplied by the
MSL in seconds has a value greater than 2^32.)
The default MSL value is 120 seconds
(defined as half the value of the
By default, large window scaling and timestamps are enabled
on all interfaces provided that the inconfig
tcp_do_rfc1323 parameter is set to 1.
This behavior should be turned off using the -rfc1323 command
for SLIP and PPP interfaces that use header compression.
Turn off TCP large window scaling and timestamps
(RFC 1323) for an interface.
This should be specified for SLIP and
PPP interfaces if they use header compression.
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 reinitialized.
Messages indicating the
specified interface does not exist, or the requested
address is unknown, or the user is not privileged and tried
to alter an interface's configuration.
The debug and link-specific parameters are driver dependent and may or may
not produce any useful results when used on a given interface. See
for a discussion of any functionality that a generic kernel may support.
Only root may modify the configuration of a network interface.
© 2004 The SCO Group, Inc. All rights reserved.
UnixWare 7 Release 7.1.4 - 25 April 2004