Iptables default log file
For example, if you type the following command, it will display current iptables log from /var/log/messages file:
# tail -f /var/log/messages
Output:
Oct 4 01:14:19 debian kernel: IN=ra0 OUT= MAC=00:17:9a:0a:f6:44:00:08:5c:00:00:01:08:00 SRC=200.142.84.36 DST=192.168.1.2 LEN=60 TOS=0x00 PREC=0x00 TTL=51 ID=18374 DF PROTO=TCP SPT=46040 DPT=22 WINDOW=5840 RES=0x00 SYN URGP=0
Oct 4 00:13:55 debian kernel: IN=ra0 OUT= MAC=ff:ff:ff:ff:ff:ff:00:18:de:55:0a:56:08:00 SRC=192.168.1.30 DST=192.168.1.255LEN=78 TOS=0x00 PREC=0x00 TTL=128 ID=13461 PROTO=UDP SPT=137 DPT=137 LEN=58
Procedure to log the iptables messages to a different log file
Open your /etc/syslog.conf file:
# vi /etc/syslog.conf
Append following line ：
kern.warning /var/log/iptables.log
Save and close the file.
Restart the syslogd (Debian / Ubuntu Linux):
# /etc/init.d/sysklogd restart On the other hand, use following command to restart syslogd under Red Hat/Cent OS/Fedora Core Linux:
# /etc/init.d/syslog restart
Now make sure you pass the log-level 4 option with log-prefix to iptables. For example:
# DROP everything and Log it
iptables -A INPUT -j LOG -–log-level 4
iptables -A INPUT -j DROP
For example, drop and log all connections from IP address 64.55.11.2 to your /var/log/iptables.log file:
iptables -A INPUT -s 64.55.11.2 -m limit --limit 5/m --limit-burst 7 -j LOG -–log-prefix ‘** HACKERS **’ --log-level 4
iptables -A INPUT -s 64.55.11.2 -j DROP
Where,
* --log-level 4: Level of logging. The level # 4 is for warning.
* --log-prefix ‘*** TEXT ***’: Prefix log messages with the specified prefix (TEXT); up to 29 letters long, and useful for distinguishing messages in the logs.
You can now see all iptables message logged to /var/log/iptables.log file:
# tail -f /var/log/iptables.log
例如
iptables -t nat -A POSTROUTING -s 192.168.10.128/25 -o eht0 -j MASQUERADE
iptables -A FORWARD -p tcp -j LOG --log-level info --log-tcp-optinos
iptables -A input -i eth0 -p tcp -j LOG --log-level info --log-prefix "IPTABLES TCP-IN:"