How to configure my firewall

144419855310001 · 08-16-2006, 09:27 AM

1) I am running Fedora Core 5 86_64 and was wondering whether anyone could point me in the direction of a good script to set up my firewall. Its accidentally in a rather permissive mode at the moment as a result of me fiddling with it!

I need access for my wireless and wired ethernet card, my modem & internet access, etc. (Wouldn't want to lock myself out of these). I think setting up a firewall myself (even with such tools as Webmin, which I just downloaded) is beyond my scope.

Any suggestions?

2) I was also wondering about SELinux. I had to turn off SELinux sometime ago in order to get vmware to work.
Somebody said:

Quote:

Just get rid of SELinux. Dozens of mysterious problems will suddenly disappear and your TCO will be much lower

What do you think? Exactly how much performance do I save by turining off SELinux?

pljvaldez · 08-16-2006, 11:39 AM

1) If it's a desktop, I'd try using a gui like firestarter. It's a stateful firewall and you can set it up such that it will prompt you as you use services to allow or disallow them. So when a machine tries to connect, you can just click "Allow this service from this machine".

2) Don't know much about it.

win32sux · 08-16-2006, 12:41 PM

here's a simple script that will set your policies, clear your tables, and set your rules...

Code:

#!/bin/sh

IPT="/sbin/iptables"

$IPT -P INPUT DROP
$IPT -P FORWARD DROP
$IPT -P OUTPUT ACCEPT

$IPT -t mangle -P PREROUTING ACCEPT
$IPT -t mangle -P INPUT ACCEPT
$IPT -t mangle -P FORWARD ACCEPT
$IPT -t mangle -P OUTPUT ACCEPT
$IPT -t mangle -P POSTROUTING ACCEPT

$IPT -t nat -P PREROUTING ACCEPT
$IPT -t nat -P POSTROUTING ACCEPT
$IPT -t nat -P OUTPUT ACCEPT

$IPT -F
$IPT -F -t nat
$IPT -F -t mangle

$IPT -X
$IPT -X -t nat
$IPT -X -t mangle

$IPT -A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
$IPT -A INPUT -i lo -j ACCEPT

this script blocks all incoming connections - it's what is commonly called a "stealth firewall script"... it's also super simple, as the only actual *rules* are those two which appear in bold... this script will work no matter what your interfaces are called, or how many you have...

after executing the script, i believe you save the configuration (on red hat distros) by doing a:

Code:

service iptables save

just my

...

144419855310001 · 08-17-2006, 09:44 AM

Quote:

If it's a desktop, I'd try using a gui like firestarter.

Thanks. This sounds great.

Quote:

this script blocks all incoming connections - it's what is commonly called a "stealth firewall script"...

Thank you also! Will this block incoming internet connections through my wireless card though?

win32sux · 08-17-2006, 12:33 PM

Quote:

Originally Posted by 144419855310001

Thank you also! Will this block incoming internet connections through my wireless card though?

yes, because the rule doesn't specify any interface, it will block incoming connections on all your interfaces...

144419855310001 · 08-18-2006, 07:58 AM

Quote:

yes, because the rule doesn't specify any interface, it will block incoming connections on all your interfaces...

Looks like I'll have to do some further reading then. I'll see how I go with firestarter too.

simcox1 · 08-19-2006, 08:20 AM

If you want to open a specific incoming port, you can do it something like this.

$IPT -A INPUT -p tcp --dport 25 -i eth0 -j ACCEPT

Which you can add at the end. That specifies that 'port 25' (smtp) is open for the interface called 'eth0'.

win32sux · 08-19-2006, 09:39 AM

Quote:

Originally Posted by simcox1

If you want to open a specific incoming port, you can do it something like this.

$IPT -A INPUT -p tcp --dport 25 -i eth0 -j ACCEPT

Which you can add at the end. That specifies that 'port 25' (smtp) is open for the interface called 'eth0'.

if you're using the script above, it would be a good idea to use the state table for this also, otherwise you're just allowing packets of any state (which kinda defeats the purpose of stateful filtering):

Code:

$IPT -A INPUT -p TCP -i $IFACE --dport 25 \
-m state --state NEW -j ACCEPT

where $IFACE is the interface you want the rule to apply to...