Closing Ports

KiLLaWaBBiT · 12-10-2004, 04:17 AM

Could anyone please tell me how to close ports manually, having a nightmare here! Many thanx for any replies.

syl20 · 12-10-2004, 04:43 AM

Hi KiLLaWaBBiT
to close port, turn off daemon using ports you want to close.
To close port 25, turn off smtpd.

bathory · 12-10-2004, 05:14 AM

Also open /etc/inetd.conf (or /etc/xinetd.conf) and comment out all the services you don't need. Then restart inetd (or xinetd)

sigsegv · 12-10-2004, 09:46 PM

iptables -I INPUT -j DROP would do it nicely. Note that this will close *all* ports though.

sh1ft · 12-10-2004, 11:23 PM

To close a specific port you could do:

Code:

iptables -A INPUT -p tcp -dport 21 -j DROP

For example. Use the man pages to see what this means, the ones for iptables are surprisingly good.

cormander · 12-17-2004, 08:07 PM

Quote:

Originally posted by sigsegv
iptables -I INPUT -j DROP would do it nicely. Note that this will close *all* ports though.

It is generally a good idea to do this at the bottom of your iptables firewall script. This is called a "deny-by-default" policy.

Make sure you open all the desired ports before this entry:

Code:

 iptables -A INPUT -p tcp -dport 21 -j ACCEPT

etc

-Corey

sigsegv · 12-17-2004, 08:53 PM

In the interest of accuracy, it's a rule that DENYs all packets on INPUT that cross it. The default policy is something else entirely, and a "deny by default" policy would be accomplished like so:

Code:

# Flush old rules
iptables -F
iptables -t nat -F
iptables -t mangle -F

# Set default action (policy)
iptables -P INPUT DROP
iptables -P FORWARD DROP
iptables -P OUTPUT DROP

# Put rules to do something useful here