Tag: iptables

  • Force iptables to log messages to a different log file

    According to man page:
    Iptables is used to set up, maintain, and inspect the tables of IP packet filter rules in the Linux kernel. Several different tables may be defined. Each table contains a number of built-in chains and may also contain user defined chains.

    By default, Iptables log message to a /var/log/messages file. However you can change this location. I will show you how to create a new logfile called /var/log/iptables.log. Changing or using a new file allows you to create better statistics and/or allows you to analyze the attacks.

    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 00:44:28 debian gconfd (vivek-4435): Resolved address \"xml:readonly:/etc/gconf/gconf.xml.defaults\" to a read-only configuration source at position 2
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 restartOn 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

    Updated for accuracy.