1) Backup existing /etc/sysconfig/iptables
cp /etc/sysconfig/iptables /etc/sysconfig/iptables.pre-LOGNEW-start
2) Save running iptables config
service iptables save
3) Backup running /etc/sysconfig/iptables
cp /etc/sysconfig/iptables /etc/sysconfig/iptables.pre-LOGNEW-running
4) Create a new iptables chain called 'LOGNEW'
iptables -N LOGNEW
iptables -I LOGNEW 1 -m limit --limit 2/min -j LOG --log-prefix "iptables-new: "
#iptables -I LOGNEW 1 -m iprange --src-range 127.0.0.1-127.0.0.255 -j RETURN # disables logging loopbacks
#iptables -I LOGNEW 1 -m iprange --dst-range 223.0.0.1-223.0.0.255 -j RETURN # disables logging multicasts
#iptables -I LOGNEW 1 -m iprange --dst-range 224.0.0.1-224.0.0.255 -j RETURN # disables logging multicasts
5) For all INPUT packets, forward 'NEW' connections to the 'LOGNEW' chain
iptables -I INPUT 1 -m state --state NEW -j LOGNEW
6) Save running iptables config
service iptables save
7) Validate running iptable config
service iptables restart
iptables -S
Verify the following lines exist in the output of iptables -S:
...
-N LOGNEW
-A INPUT -m state --state NEW -j LOGNEW
...
-A LOGNEW -m limit --limit 2/min -j LOG --log-prefix "iptables-new: "
Check the output of /var/log/messages
grep iptables-new: /var/log/messages
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INSTALL METHOD #2 - manually modify /etc/sysconfig/iptables
1) Backup existing /etc/sysconfig/iptables
cp /etc/sysconfig/iptables /etc/sysconfig/iptables.pre-LOGNEW-start
2) Edit /etc/sysconfig/iptables
vi /etc/sysconfig/iptables
Below the line starts with ":OUTPUT ACCEPT *", add the following line
:LOGNEW - [0:0]
As the very first statement to the INPUT filter (lines beginning with "-A INPUT ..."), add the following line
-A INPUT -m state --state NEW -j LOGNEW
Above the line begins with "COMMIT", or below the very last statement to the FORWARD filters (lines beginning with "-A FORWARD"), add the following line
# to filter noise, add RETURN (don't log) statements prior to -j LOG
-A LOGNEW -m limit --limit 2/min -j LOG --log-prefix "iptables-new: "
REMOVAL METHOD #1 - with iptables running (live update)
1) Remove the INPUT rule
iptables -D INPUT -m state --state NEW -j LOGNEW
2) Remove the LOGNEW links
while `iptables -D LOGNEW 1`; do iptables -D LOGNEW 1; done
3) Remove the LOGNEW chain
iptables -X LOGNEW
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