Close all ports except for one on a Debian machine

Question

I wish to set up a secure home file server on a Debian computer. I will be using my own server software that utilizes only a single TCP port. To make sure that the machine is fully secure, I'm thinking that I should close all ports except for the one my protocol is running on (such that no other protocol can be used or accessed on the machine).

Does anyone know what the best way is to close all of the ports except for one?

Answer 1

You can set the default iptables policy so that it only accepts communication from certain ports (or a range of ports):

## Drop all incoming traffic on all ports

iptables -P INPUT DROP
## Allow connections from one port
## Do not include brackets when entering the following variables, 
## [portnum] is just 80 not [80]
## [interface] == default network interface (such as eth0)
## [protocol] == the protocol you want, such as tcp, udp, and etc
## [portnum] == port number, such as 80, 443, and etc

iptables -A INPUT -i [interface] -p [protocol] --dport [portnumb] -J ACCEPT

## Allow a range of ports, such as ports 1001-1005

iptables -A INPUT -i [interface] -p [protocol] --dport [portnum]:[portnum] -J ACCEPT

Hope this helps.