re: question about ifup and ifconfig

[Ren Weili]

i have my laptop so:
/etc/init.d/networkings:
  case "$1" in
    start)
        doopt spoofprotect yes
        doopt syncookies no
        doopt ip_forward no

        echo -n "Configuring network interfaces: "
        echo "please select your environment:"
        echo "[1]:home"
        echo "[2]:office"
        read home_office
        if [ $home_office -eq "1" ]; then
                ifup -a -i /etc/network/interfaces.home 
                rm -f /etc/resolv.conf
                ln -s /etc/resolv.conf.home /etc/resolv.conf
                rm -f /etc/apt/apt.conf
        elif [ $home_office -eq "2" ]; then
                ifup -a -i /etc/network/interfaces.office               
                rm -f /etc/resolv.conf
                ln -s /etc/resolv.conf.office /etc/resolv.conf
                if [ ! -f /etc/apt/apt.conf ]; then
                        ln -s /etc/apt/apt.conf.office
/etc/apt/apt.conf       
                fi
        fi
        echo "done."
        ;;

and it works good.
my question here is: 
        1) is ifup/ifdown written in c and realized a set function of
ifconfig and add route table?
        2) how can i use ifconfig to bring up eth0 with dhcp?


thanks