IP-Range and Subnetmask

hi

i´ve a simple question

is it possible to prevent spoofing attacks to 172.16.0.0-172.31.255.255 on the external internet IP in one rule?

something like that

iptables -A INPUT -p tcp -s 172.16.0.0/255.31.0.0 -d $INET_IP -i ppp0 -j SPOOFED

???

but i think the rule above is wrong
so: is it possible at all?
or do i have to write a loop or all single ip-ranges manually?

thx
greez