Two methods can be used to bring interfaces up or down.
Usage:
| # ip link set dev <interface> up # ip link set dev <interface> down | 
Example:
| # ip link set dev eth0 up # ip link set dev eth0 down | 
Usage:
| # /sbin/ifconfig <interface> up # /sbin/ifconfig <interface> down | 
Example:
| # /sbin/ifconfig eth0 up # /sbin/ifconfig eth0 down |