dport is not working on iptables command

Question

In terminal I type :

iptables -A INPUT --dport 443 -j DROP

And it tells me :

iptables v1.4.21: unknown option "--dport"

what is wrong with --dport?

Solution

You probably need to first identify the protocol, for example TCP or UDP. You do that by using the -p <protocol> option.

I'm assuming you want TCP, so your iptables command should look like this:

iptables -A INPUT -p tcp --dport 443 -j DROP