How to disable a port, such as 21?

iclinux · 01-10-2005, 03:23 AM

Hi there,

I want to write a program that can disable specified ports, such as 21, 80. But I don't know how to do it.

Will you please make a suggestion for me? Thanks a lot.

maxut · 01-10-2005, 04:48 AM

what do u mean by disabling a specified port?
if u mean "blocking port", u can do that with iptables:

#iptables -I INPUT -p tcp --dport 21 -j REJECT

good luck.

Cedrik · 01-10-2005, 04:48 AM

These are 2 firewall rules for iptables that block your specified TCP ports 21 and 80 for your
eth0 interface :

iptables -A INPUT -i eth0 -p tcp --dport 21 -j DROP
iptables -A INPUT -i eth0 -p udp --dport 80 -j DROP

But if you don't run a ftp server and a web server, these ports should not be open in your
machine