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