linux command to prevent dos attack by using netstat and iptables

Best you can do , IMO, is to set limits

sudo iptables -A INPUT -m limit --limit 50/minute --limit-burst 200 -j ACCEPT
sudo iptables -A INPUT -j REJECT

For port 80, use

sudo iptables -A INPUT -p tcp --dport 80 -m state --state NEW -m limit --limit 50/minute --limit-burst 200 -j ACCEPT
sudo iptables -A INPUT -m state --state RELATED,ESTABLISHED -m limit --limit 50/second --limit-burst 50 -j ACCEPT
sudo iptables -A INPUT -j REJECT