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skimpydog

IPTABLES

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Joined: 2007/6/10

From Dallas, TX

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iptables is really quite a responsibility to maintain.

In too many regards it is not necessary to block entire countries, or to allow only specified countries.
-- This can put a strain on your server - and it is not good practice.
--- There are other applications such as APF to take care of things dynamically

A Few basic tips for applying, and removing iptables rules are as follows:

Allow a few basic services:

/sbin/iptables -A INPUT -p icmp -i eth0 -j ACCEPT
/sbin/iptables -A INPUT -p tcp -m tcp -i eth0 --dport 20:21 -j ACCEPT
/sbin/iptables -A INPUT -p tcp -m tcp -i eth0 --dport 80 -j ACCEPT
/sbin/iptables -A INPUT -p tcp -m tcp -i eth0 --dport 22 -j ACCEPT
/sbin/iptables -A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
/sbin/iptables -A INPUT -s 127.0.0.1 -j ACCEPT
/sbin/iptables -A INPUT -j REJECT

Save your settings (2 ways - depends on your Linux/UNIX flavor):
1:

/sbin/iptables-save > /etc/sysconfig/iptables

/sbin/service iptables save

Let's say I want to allow udp port 27960 to line 5:

/sbin/iptables -I INPUT 5 -p udp -m udp -i eth0 --dport 27960 -j ACCEPT

-- Again, don't forget to save your settings!

If you are running RHEL, CENTOS, Fedora - Redhat flavors, you may make sure the service starts upon reboot as it should, by doing:

/sbin/chkconfig iptables on

-- This will allow iptables to start on all run levels.

If you want to view the iptables rules, again you have 2 options here depending on your flavor:
1:

/sbin/iptables --list
Chain INPUT (policy ACCEPT)
target     prot opt source               destination
ACCEPT     icmp --  anywhere             anywhere
ACCEPT     tcp  --  anywhere             anywhere            tcp dpts:ftp-data:ftp
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:http
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:rockwell-csp2
ACCEPT     udp  --  anywhere             anywhere            udp dpt:27960
ACCEPT     all  --  anywhere             anywhere            state RELATED,ESTABLISHED
ACCEPT     all  --  localhost.localdomain.domain  anywhere
REJECT     all  --  anywhere             anywhere            reject-with icmp-port-unreachable

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination

/sbin/service iptables status
Table: filter
Chain INPUT (policy ACCEPT)
num  target     prot opt source               destination
1    ACCEPT     icmp --  0.0.0.0/0            0.0.0.0/0
2    ACCEPT     tcp  --  0.0.0.0/0            0.0.0.0/0           tcp dpts:20:21
3    ACCEPT     tcp  --  0.0.0.0/0            0.0.0.0/0           tcp dpt:80
4    ACCEPT     tcp  --  0.0.0.0/0            0.0.0.0/0           tcp dpt:2222
5    ACCEPT     udp  --  0.0.0.0/0            0.0.0.0/0           udp dpt:27960
6    ACCEPT     all  --  0.0.0.0/0            0.0.0.0/0           state RELATED,ESTABLISHED
23   ACCEPT     all  --  127.0.0.1            0.0.0.0/0
24   REJECT     all  --  0.0.0.0/0            0.0.0.0/0           reject-with icmp-port-unreachable

Chain FORWARD (policy ACCEPT)
num  target     prot opt source               destination

Chain OUTPUT (policy ACCEPT)
num  target     prot opt source               destination

Posted on: 2008/10/4 17:08