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Old 08-25-2010, 10:43 PM   #1
Registered: Aug 2009
Distribution: linux
Posts: 527

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A question regarding iptables rules and OUTPUT filters


I put together the following filter set :

###To understand this script, reference the No Starch Press Linux Firewalls Book.


### flush / drop policy sets
echo "[+] Flushing existing rules with DEFAULT of DROP [+]"
echo "[+] IPv4 [+]"
	$IPT -F
	$IPT -F -t nat
	$IPT -X

echo "[+] IPv6 [+]"
	$IPT6 -F
	$IPT6 -F -t nat
	$IPT6 -X
###Module Loading: many of these may already be loaded. Also, running lsmod will aide in tracking down issues with module loading.
echo "[+] Loading modules for state tracking [+]"
	$MODPROBE ip_conntrack
	$MODPROBE iptable_nat
	$MODPROBE ip_conntrack_ftp
	$MODPROBE ip_nat_ftp

###INPUT rules: Allowing only ESTABLISHED / RELATED 
echo "[+] Setting up INPUT table [+]"
	$IPT -A INPUT -m conntrack --ctstate INVALID -j LOG --log-prefix "DROP INVALID" --log-ip-options --log-tcp-options
	$IPT -A INPUT -m conntrack --ctstate INVALID -j DROP	
	$IPT -A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
###INPUT rules: anti-spoofing rules. How to set up anti-spoofing rules on single-homed system.

###INPUT rules: INPUT from internal network, or specific services.
        $IPT -A INPUT -p tcp -m multiport --ports 137:139,445 -j ACCEPT
        $IPT -A INPUT -p udp -m multiport --ports 13:139,445 -j ACCEPT
###INPUT rules: LOG rules.
	$IPT -A INPUT -i ! lo -j LOG --log-prefix "DROP" --log-ip-options --log-tcp-options
echo "[+] Done [+]"

###OUTPUT rules
echo "[+] Setting up OUTPUT table [+]"
	$IPT -A OUTPUT -m conntrack --ctstate INVALID -j LOG --log-prefix "DROP INVALID" --log-ip-options --log-tcp-options
	$IPT -A OUTPUT -m conntrack --ctstate INVALID -j DROP

###OUTPUT rules: Allowed out
	$IPT -A OUTPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
	$IPT -A OUTPUT -p tcp --dport 21 --syn -m conntrack --ctstate NEW -j ACCEPT
	#$IPT -A OUTPUT -p tcp --dport 22 --syn -m conntrack --ctstate NEW -j ACCEPT
	$IPT -A OUTPUT -p tcp --dport 25 --syn -m conntrack --ctstate NEW -j ACCEPT
	$IPT -A OUTPUT -p tcp --dport 43 --syn -m conntrack --ctstate NEW -j ACCEPT
	$IPT -A OUTPUT -p tcp --dport 80 --syn -m conntrack --ctstate NEW -j ACCEPT
	$IPT -A OUTPUT -p tcp --dport 443 --syn -m conntrack --ctstate NEW -j ACCEPT
	$IPT -A OUTPUT -p tcp --dport 4321 --syn -m conntrack --ctstate NEW -j ACCEPT
	$IPT -A OUTPUT -p tcp --dport 53 -m conntrack --ctstate NEW -j ACCEPT
	$IPT -A OUTPUT -p icmp --icmp-type echo-request -j ACCEPT
	$IPT -A OUTPUT -p udp --dport 53 -m conntrack --ctstate NEW -j ACCEPT
	$IPT -A OUTPUT -p tcp -m multiport --ports 137:139,445 -j ACCEPT
        $IPT -A OUTPUT -p udp -m multiport --ports 137:139,445 -j ACCEPT
###OUTPUT rules: LOG rule
	$IPT -A OUTPUT -o ! lo -j LOG --log-prefix "DROPED OUTBOUND" --log-ip-options --log-tcp-options
I wanted to know how to allow certain APPLICATIONS through the OUTBOUND tables. For example, I wish to be able to use tools such as nmap,tracepath, and traceroute. However, I am not sure where to look to understand the ports to open. I was starting to think that maybe rather than ports to open it would need to be somehthing like tcp flags that would ned to be allowed. Any way, I have tried google and am still haing problems.
I started wanting to use these tools due to getting ready for my network+ and security+ certs. I would really appreciate the help.
Old 08-27-2010, 06:39 PM   #2
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/etc/services normally contains a fairly complete list of ports used by standard services. I think there is at least one version that is vetted by IANA or some such organization.

--- rod.
1 members found this post helpful.
Old 08-27-2010, 10:29 PM   #3
Registered: Aug 2009
Distribution: linux
Posts: 527

Original Poster
Rep: Reputation: 51
thanks man. Guess I should have looked at some man pages. Nmap at least seems to be --source-port ( wow.. ) . thanks for trying to address my stupid question.



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