Linux Command - ifconfig

Ifconfig 
This command is used to configure the network interfaces on the Linux system. The configuration files for each Ethernet Interfaces will be in the below location

/etc/sysconfig/network-scripts/

Syntax:  

# ifconfig [interface]

Example: The below command will display the information of the first “Ethernet Interface”.

# ifconfig eth0

"ifconfig" command without any option will list all the active Ethernet connections.

# ifconfig

This command with "-a" option list all the interfaces including interfaces which are down.

# ifconfig –a

Eth0 – First Ethernet Interface
Lo – Lookback Interface
Sit0 – First Simple interface Traslation

How to bring the specific network interface up and down?
Syntax: 

# ifconfig [interface] down/up

Example: 

# ifconfig eth0 down
# ifconfig eth0 up

# ifdown [OPTIONS] interface-card

Example:

# ifdown eth0
# ifdown eth0:1

# ifup [OPTIONS] interface-card

Example:

# ifup eth0
# ifup eth0:1

Type "man ifconfig" for more information about the this command.