# simple IP arithmetic functions:

function quad2num()

{

    if [ $# -eq 4 ]; then

       let n="$1<<24|$2<<16|$3<<8|$4"

       echo $n;

       return 0;

    fi

    echo '0';

    return 1;

}

function ip2num()

{

    IFS='.' quad2num $1;

}

function num2ip()

{

    let n="$1";

    let o1='(n>>24)&0xff';

    let o2='(n>>16)&0xff';

    let o3='(n>>8)&0xff';

    let o4='n & 0xff';

    echo $o1.$o2.$o3.$o4;

}

function mask()

{   

    ip=$1

    m=$2

    let ip=`IFS='.' ip2num $ip`;

    let m=`IFS='.' ip2num $m`;

    let n='ip&m';

    num2ip $n;

}

function routerReachable()

{ # Handle silly DHCP servers that give us a router not on our subnet:    

    router=$1

    routerSubnet=`mask $router $new_subnet_mask`

    mySubnet=`mask $new_ip_address $new_subnet_mask`

    unreachable=0

    if [ "$routerSubnet" != "$mySubnet" ]; then

	unreachable=1

	if /sbin/arping -f -q -I $interface -w2 $router; then

	    /sbin/route add ${router}/32 dev $interface

	    if [ $? -eq 0 ]; then

		unreachable=0

	    fi

	else

	    unreachable=1

	fi;

    fi;

    return $unreachable;

}

function add_default_gateway()

{

    router=$1

    metric=$2

    if routerReachable $router ; then

	/sbin/route add default gw $router $metric dev $interface;

	return $?;

    fi;

    return 1;

}