Displays the network interface's configuration, characteristics and statistics

syntax : 

   ifconfig [ interface name ]

example : 

  $ ifconfig eth0 

  eth0 Link encap: Ethernet HWaddr 00:00:C0:9A:72:CA

   inet addr:172.16.5.3 Bcast:172.16.5.255 Mask:255.255.255.0

   UP BROADCAST NOTRAILERS RUNNING MTU:1500 Metric:1 

   RX packets:22283 errors:0 dropped:0 overruns:0 frame:0

   TX packets:12321 errors:0 dropped:0 overruns:0 carrier:0

   collision:26 txqueuelen:100

   RX bytes: 32702095 (31.1 Mb) TX bytes: 841990 (822.2 Kb)

   Interrupt:5 Base address: 0x250 Memory: c0000-c2000

Things to Know ?

UP 

   the said interface is enabled.   Use the ifconfig command to manually mark the interface

   DOWN only when changing a configuration value, such as the IP address.

   # ifconfig eth0 down

   # ifconfig eth0 172.16.5.9 up

NOTRAILERS 

   the said interface does not use trailer encapsulation.   

   Trailer encapsulation was a technique used to speed the process of Ethernet packets on early network computers.   

   It's not use anymore on modern systems

BROADCAST 

   the said interface supports broadcasts.   some physical networks, such as Ethernet, provide built-in support for broadcasting packets

RUNNING 

   the said interface is operational.   The interface must be RUNNING at all times.   

   If it isn't, the driver for this interface may not be properly installed

MTU 

   the maximum transmission unit used by this interface.   In the example, it is 1500 bytes, which is the standard for Ethernet 

Metric 

   the routing cost associated with this interface.   In the example, it is 1, which is the normal cost associated with all network interfaces

PROMISC 

   the interface is set to promiscuous mode.   Promiscuous mode means that the interface accepts all packets and sends them all up to IP for processing.   

   This feature is required by the tcpdump tool.

   # ifconfig eth0 down

   # ifconfig eth0 -promisc up