After testing and looking at the kernel source, I realize that this mapping:
iptables -t nat -I PREROUTING -p tcp -m tcp --dport 30000:40000 -j DNAT --to [local_ip]:10000-2000
Doesn't do a one-to-one port mapping
126.96.36.199:30000 > 192.168.0.5:10000
188.8.131.52.30001 > 192.168.0.5:10001
184.108.40.206.30002 > 192.168.0.5:10002
I was wondering if it was possible to do the 1:1 port range forwarding to different port ranges or if you have to use individual rules.