BDS version here

ifconfig - configure a network interface
see also ethtool

ifconfig [interface [aftype] options | adress ... ]

At boot time to set up interfaces, after that, needed when debugging or tuning .

Without arguments displays the status of the currently active interfaces.

If a single interface is given displays the status of that interface only;

-a displays the status of all interfaces, even those that are down.

With an interface and options, configures that interface.

Address Families If the first argument after the interface name is an address family, it is used for decoding and displaying all protocol addresses. Address families include inet (TCP/IP, default), inet6 (IPv6), ax25 (AMPR Packet Radio), ddp (Appletalk Phase 2), ipx (Novell IPX) and netrom (AMPR Packet radio).
Numbers as parts in IPv4 dotted decimal notation may be decimal, octal ( with leading 0), or hexadecimal (leading 0x)

interfaceThe name of the interface. This is usually a driver name followed by a unit number, for example eth0 for the first Ethernet interface.
address Set the IP address
up activates the interface implicitly specified if an address is assigned to the interface.
down causes the driver for this interface to be shut down.
netmask addr Set the IP network mask for this interface.
This value defaults to the usual class A, B or C network mask (as derived from the interface IP address), but it can be set to other values.

For example if the IP address is 192.168.1.4 a netmask of 255.255.255.0 would specify that all nodes which begin with 192.168.1 are in the same subnet and no gateway device need be contacted to send packets. Packets destined for nodes that do not begin with 192.168.1 must first be directed to the gateway which then forwards the packets to another network which (eventually) can send the packets to the subnet containing the destination node.See route

[-]broadcast [addr] set the broadcast address (frequently the network address with all subnet bits set. For example with netmask of 255.255.255.0, and the network address of 192.168.3,
the broadcast address may be 192.168.3.255 . or
set (or clear) the IFF_BROADCAST flag
[-]arp enable or disable the use of the ARP (Address Resolution Protocol) on this interface.
The conversion of IP (nnn.nnn.nnn.nnn) addresses to MAC ( xx:xx:xx:xx:xx:xx:xx) addesses See arp
[-]allmulti Enable or disable all-multicast mode.
If selected, all multicast packets on the network will be received by the interface.
metric N sets the interface metric (cost for computing cheapest (fastest) route)
mtu N sets the Maximum Transfer Unit (MTU)
dstaddr addr Set the destination IP address for a point-to-point link (such as PPP).
add addr/prefixlen Add an IPv6 address
del addr/prefixlen Remove an IPv6 address
tunnel aa.bb.cc.dd Create a new SIT (IPv6-in-IPv4) device, tunnelling to the given destination.
irq addr specify the interrupt line used by this device.
io_addr addr specify the start address in I/O space for this device.
mem_start addr Specify the start address for shared memory used by this device.
media type Set the physical port or medium type to be used by the device.
values include: type 10base2 (thin Ethernet, coax), 10baseT (twisted-pair 10Mbps Ethernet)( 8 wire with RJ45 block connector>, AUI (external transceiver) .
auto can be used to tell the driver to auto-sense the media type.
[-]pointopoint [addr] enables the point-to-point mode.
a link between 2 and only 2 nodes (for example a dial up or dedicated circuit).
If the addr is given, set the address of the destination node.
Otherwise, set or clear the IFF_POINTOPOINT flag
hw class address Set the hardware address.
Hardware classes include ether (Ethernet), ax25 (AMPR AX.25), ARCnet and netrom (AMPR NET/ROM).
multicast Set the multicast flag
txqueuelen length Set the length of the transmit queue of the device.
It is useful to set this to small values for slower devices with a high latency (modem links, ISDN) to prevent fast bulk transfers from disturbing interactive traffic like telnet too much.
[-]promisc Enable or disable the promiscuous mode of the interface.
That is, all packets on the network will be received by the interface even if not addressed to this node. Used for debugging network packets. 
Usage:
  ifconfig [-a] [-v] [-s] interface 
  [[-]broadcast [address]]  
  [netmask address]  
  [outfill NN] [keepalive NN]
  [hw HW address]  
  [metric NN]  [mtu NN]
  [[-]trailers]  [[-]arp]  [[-]allmulti]
  [mem_start NN]  [io_addr NN]  [irq NN]  
  [txqueuelen NN]
  [[-]pointopoint [address]]
  [dstaddr address]  
  [[AF] address]
  [tunnel address]
  [multicast]  [[-]promisc]
  [[-]dynamic]
  [up|down] 
  [add|del address[/prefixlen]] 
  [media type]
 

  HW=Hardware Type.
    loop Local Loopback 
    slip Serial Line IP       slip6 6-bit Serial Line IP 
    cslip VJ Serial Line IP   cslip6 VJ 6-bit Serial Line IP 
    ppp Point-to-Point Protocol 
    adaptive Adaptive Serial Line IP 
    strip Metricom Starmode IP     
    ether Ethernet            ash Ash                   
    tr 16/4 Mbps Token Ring    tr 16/4 Mbps Token Ring New ax25 AMPR AX.25 
    netrom AMPR NET/ROM       rose AMPR ROSE             tunnel IPIP Tunnel 
    hdlc Cisco-HDLC           lapb LAPB 
    arcnet ARCnet             dlci Frame Relay DLCI      frad FrameRelayAccessDevice 
    sit IPv6-in-IPv4          
    fddi Fiber Distributed Data Interface          hippi HIPPI 
    irda IrLAP                 ec Econet           x25 generic X.25 
    infiniband InfiniBand     eui64 Generic EUI-64 

  AF=Address family. Default: inet
    unix (UNIX Domain)      inet (DARPA Internet)       inet6 (IPv6) 
    ax25 (AMPR AX.25)       netrom (AMPR NET/ROM)       rose (AMPR ROSE) 
    ipx (Novell IPX)        ddp (Appletalk DDP)         ec (Econet) 
    ash (Ash)               x25 (CCITT X.25)
The statistics printed for the original address are shared with all alias addresses on the same device. If you want per-address statistics you should add explicit accounting rules for the address using the ipchains(8) command.

Interrupt problems with Ethernet device drivers fail with EAGAIN. See http://www.scyld.com/expert/irq-conflict.html for more information.

FILES

/proc/net/socket, /proc/net/dev, /proc/net/if_inet6

restrictions

Appletalk DDP and IPX addresses will be displayed but cannot be altered by this command.

SEE ALSO route(8), netstat(8), arp(8), rarp(8), ipchains(8)