ifconfig Command

The ifconfig command displays information about the configuration of an interface that you specify. (Refer to the ifconfig(1M) man page for complete details.) The syntax of ifconfig is:

ifconfig interface-name [protocol_family]

If you want information about a specific interface, for example le0, type:

$ ifconfig le0

For an le0 interface, your output resembles the following:

le0: flags=863<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
 	inet 129.144.44.140 netmask ffffff00 broadcast 129.144.44.255
ether 8:0:20:8:el:fd

The flags section just given shows that the interface is configured "up," capable of broadcasting, and not using "trailer" link level encapsulation. The mtu field tells you that this interface has a maximum transfer rate of 1500. Information on the second line includes the IP address of the host you are using, the netmask being currently used, and the IP broadcast address of the interface. The third line gives the machine address (Ethernet, in this case) of the host.

A useful ifconfig option is -a, which provides information on all interfaces on your network. For example, typing ifconfig -aproduces:

le0:  flags=49<UP,LOOPBACK,RUNNING> mtu 8232
     inet 127.144.44.140 netmask ff000000 
le0:flags=863<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
     inet 129.144.44.140 netmask ffffff00 broadcast 129.144.44.255
ether 8:0:20:8:el:fd

Output that indicates an interface is not running might mean a problem with that interface. In this case, see the ifconfig(1M) man page.