I finally managed to install my VM host and now I am messing with iptables to create, test and learn.
Does it matter if i put the below rules at the begin or at the end of my rules ?
$IPT -P INPUT DROP $IPT -P FORWARD DROP $IPT -P OUTPUT DROP
i have tested and there was no difference but i would like to confirm.
Answer I choose so far: It is a good idea to apply your policies as early as possible. Put them at the start. DROP rules on internal traffic can cause problems.
Having the below rule would be considered as a fault on the firewall ?
$IPT -A OUTPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
Without this rule i would need to add for example an OUTPUT rule for my ssh connection, example:
$IPT -A OUTPUT -p tcp --sport 2013 -j ACCEPT
Answer: After more tests and talks with people on #iptables@freenode, i came to the conclusion that using
-m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPTfor INPUT and OUPUT is a fine approch and will help you deal with lots of things like for example the FTP and is a fine approch because unless you have that given port open and being accept there will be no malicious connection on it.
Here is a normal example without using the above:
$IPT -A INPUT -p tcp --dport 20:21 -j ACCEPT $IPT -A OUTPUT -p tcp --dport 20:21 -j ACCEPT
Now here is how the rule looks like using the above:
$IPT -A INPUT -p tcp --dport 21 -m conntrack --ctstate NEW -j ACCEPT
That's all you need because once the connection is ESTABLISHED, the output will follow-up right away and you won't need to make rules for the ftp-data port.
What are bad things of having the below rule, could you give some example as to why not have it and instead just define anything you may need to use ?
$IPT -P OUTPUT ACCEPT
Answer I choose so far: This policy rule allows all outgoing traffic. As a policy, allowing everything is obviously less secure than allowing only explicit kinds of traffic. So if security is your utmost priority, you'll want to set a DROP policy on the output chain instead. Just be aware that you'll then have to include a number of rules to allow outgoing traffic to a possibly large number of mundane things, such as: DNS, SMTP, IMAP, POP3, HTTP, HTTPS, etc.
What is the difference between conntrack and state in the below context ?
$IPT -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
$IPT -A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
Answer: After some research talks with people on #iptables@freenode i came to the conclusion i should be using conntrack from here on.
Technically the conntrack match supersedes - and so obsoletes - the state match. But practically the state match is not obsoleted in any way.
I would aswell appreciate good online iptables reading materials.