Problem with Arno's IPTables ruleset?
 

I just installed Slackware 9.1. First order of business was to get the firewall up so that I could get online. I found a ruleset written by someone named Arno at simplylinux dot punted dot net. (It's my first post. Evidently I'm not allowed to use URLs until the fifth post. Anywho...) Apparently, it's reasonably widely used.

It looks pretty comprehensive, although I haven't had the chance to go over the rules in detail, but I did notice one problem that I thought should be pointed out. The first rule in the INPUT chain is supposed to accept all packets originating from the loopback interface. It comes from the following line in the rc.iptables script:

$IPTABLES -A INPUT -i lo -j ACCEPT

However, apparently my system didn't recognize "lo" (I'm guessing), and the first rule in my INPUT chain ended up accepting all packets from all sources regardless of protocol. Not much of a firewall, that. Once I changed the rule to read

$IPTABLES -A INPUT -s 127.0.0.1 -j ACCEPT

it worked as expected.

Actually, that rule means ACCEPT everything coming in on lo interface, regardless of where it came from...

So, yes it's an open ACCEPT...

It should read: $IPTABLES -A INPUT -i lo -s 127.0.0.0/8 -j ACCEPT