What is wrong with this chain

Hello List,
I want to drop portscans and DOS attacks. I've found two chains on the internet. But after executing them my connection drops and no data passes firewall. Anyone can tell me where i'm wrong?

# Log and drop portscans:
echo -n "SCAN "
$IPTABLES -A SCAN -m limit --limit 30/m -j LOG --log-prefix "PORTSCAN " --log-ip-options --log-tcp-options --log-level 1 $IPTABLES -A SCAN -j DROP

# Log and drop DOS attacks:
echo -n "DOS "
$IPTABLES -A DOS -p tcp --syn -m limit -j LOG --log-prefix "SYN Flood " $IPTABLES -A DOS -p icmp -m limit -j LOG --log-prefix "PING Flood " $IPTABLES -A DOS -j DROP

Best regards,
 ITM                          mailto:[email protected]