Ubuntu Manpage: logging - Shorewall logging

NAME

       logging - Shorewall logging

SYNOPSIS

       action:level

       NFLOG(nflog-parameters)

       ULOG(ulog-parameters)

DESCRIPTION

       The disposition of packets entering a Shorewall firewall is determined by one of a number
       of Shorewall facilities. Only some of these facilities permit logging.

        1. The packet is part of an established connection. While the packet can be logged using
           LOG rules in the ESTABLISHED section of /etc/shorewall/rules[1], that is not
           recommended because of the large amount of information that may be logged.

        2. The packet represents a connection request that is related to an established
           connection (such as a data connection associated with an FTP control connection[2]).
           These packets may be logged using LOG rules in the RELATED section of
           shorewall-rules(5)[1].

        3. The packet is rejected because of an option in shorewall.conf[3](5) or
           shorewall-interfaces(5)[4]. These packets can be logged by setting the appropriate
           logging-related option in /etc/shorewall/shorewall.conf[3].

        4. The packet matches a rule in shorewall-rules[1](5). By including a syslog level (see
           below) in the ACTION column of a rule (e.g., “ACCEPT:info net $FW tcp 22”), the
           connection attempt will be logged at that level.

        5. The packet doesn't match a rule so it is handled by a policy defined in
           shorewall-policy(5)[5]. These may be logged by specifying a syslog level in the LOG
           LEVEL column of the policy's entry (e.g., “loc net ACCEPT info”).

DEFAULT LOGGING

       By default, Shorewall directs Netfilter to log using syslog (8). Syslog classifies log
       messages by a facility and a priority (using the notation facility.priority).

       The facilities defined by syslog are auth, authpriv, cron, daemon, kern, lpr, mail, mark,
       news, syslog, user, uucp and local0 through local7.

       Throughout the Shorewall documentation, the term level rather than priority is used, since
       level is the term used by Netfilter. The syslog documentation uses the term priority.

SYSLOG LEVELS

Syslog levels are a method of describing to syslog (8) the importance of a message. A
number of Shorewall parameters have a syslog level as their value.

Valid levels are:
7 - debug (Debug-level
messages)
6 - info
(Informational)
5 - notice (Normal but
significant Condition)
4 - warning (Warning
Condition)
3 - err (Error
Condition)
2 - crit (Critical
Conditions)
1 - alert (must be handled
immediately)
0 - emerg (System is
unusable)

For most Shorewall logging, a level of 6 (info) is appropriate. Shorewall log messages are
generated by Netfilter and are logged using the kern facility and the level that you
specify. If you are unsure of the level to choose, 6 (info) is a safe bet. You may specify
levels by name or by number.

Beginning with Shorewall 4.5.5, the level name or number may be optionally followed by a
comma-separated list of one or more log options. The list is enclosed in parentheses. Log
options cause additional information to be included in each log message.

Valid log options are:

ip_options
Log messages will include the option settings from the IP header.

macdecode
Decode the MAC address and protocol.

tcp_sequence
Include TCP sequence numbers.

tcp_options
Include options from the TCP header.

uid
Include the UID of the sending program; only valid for packets originating on the
firewall itself.

Example: info(tcp_options,tcp_sequence)

Syslogd writes log messages to files (typically in /var/log/*) based on their facility and
level. The mapping of these facility/level pairs to log files is done in /etc/syslog.conf
(5). If you make changes to this file, you must restart syslogd before the changes can
take effect.

Syslog may also write to your system console. See Shorewall FAQ 16[6] for ways to avoid
having Shorewall messages written to the console.

CONFIGURING A SEPARATE LOG FOR SHOREWALL MESSAGES (ULOGD)

       There are a couple of limitations to syslogd-based logging:

        1. If you give, for example, kern.info its own log destination then that destination will
           also receive all kernel messages of levels 5 (notice) through 0 (emerg).

        2. All kernel.info messages will go to that destination and not just those from
           Netfilter.

        3. Netfilter (Shorewall) messages show up in dmesg.

       If your kernel has NFLOG target support (and most vendor-supplied kernels do), you may
       also specify a log level of NFLOG (must be all caps). When NFLOG is used, Shorewall will
       direct Netfilter to log the related messages via the NFLOG target which will send them to
       a process called “ulogd”. The ulogd program is included in most distributions.

           Note
           The NFLOG logging mechanism is completely separate from syslog. Once you switch to
           NFLOG, the settings in /etc/syslog.conf have absolutely no effect on your Shorewall
           logging (except for Shorewall status messages which still go to syslog).

       You will need to change all instances of log levels (usually “info”) in your Shorewall
       configuration files to “NFLOG” - this includes entries in the policy, rules and
       shorewall.conf files. If you initially installed using Shorewall 5.1.2 or later, you can
       simply change the setting of LOG_LEVEL in shorewall.conf.

UNDERSTANDING THE CONTENTS OF SHOREWALL LOG MESSAGES

       For general information on the contents of Netfilter log messages, see
       http://logi.cc/en/2010/07/netfilter-log-format/.

       For Shorewall-specific information, see FAQ #17[7].

CUSTOMIZING THE CONTENT OF SHOREWALL LOG MESSAGES

       In a Shorewall logging rule, the log level can be followed by a log tag as in
       "DROP:NFLOG:junk". The generated log message will include "chain-name junk DROP".

       By setting the LOGTAGONLY option to Yes in shorewall.conf(5)[8] or shorewall6.conf(5)[9],
       the disposition ('DROP' in the above example) will be omitted. Consider the following
       rule:

           #ACTION                                    SOURCE          DEST           PROTO
           REJECT(icmp-proto-unreachable):notice:IPv6 loc             net            41      # who's using IPv6 tunneling

       This rule generates the following warning at compile time:
           WARNING: Log Prefix shortened to "Shorewall:IPv6:REJECT(icmp-p "
                 /etc/shorewall/rules (line 212)

       and produces the rather ugly prefix "Shorewall:IPv6:REJECT(icmp-p ".

       Now consider this similar rule:

           #ACTION                                              SOURCE          DEST           PROTO
           REJECT(icmp-proto-unreachable):notice:IPv6,tunneling loc             net            41      # who's using IPv6 tunneling

       With LOGTAGONLY=Yes, no warning is generated and the prefix becomes
       "Shorewall:IPv6:tunneling:"

       See the shorewall[6].conf man page[10] for further information about how LOGTAGONLY=Yes
       can be used.

LOG BACKENDS

       Netfilter logging allows configuration of multiple backends. Logging backends provide the
       The low-level forward of log messages. There are currently three backends:

       LOG (ipt_LOG and ip6t_LOG).
           Normal kernel-based logging to a syslog daemon.

       ULOG (ipt_ULOG)
           ULOG logging as described ablve. Only available for IPv4.

       netlink (nfnetlink_log)
           The logging backend behind NFLOG, defined above.

       The currently-available and currently-selected IPv4 and IPv6 backends are shown in
       /proc/sys/net/netfilter/nf_log:

           cat /proc/net/netfilter/nf_log
            0 NONE (nfnetlink_log)
            1 NONE (nfnetlink_log)
            2 ipt_ULOG (ipt_ULOG,ipt_LOG,nfnetlink_log)
            3 NONE (nfnetlink_log)
            4 NONE (nfnetlink_log)
            5 NONE (nfnetlink_log)
            6 NONE (nfnetlink_log)
            7 NONE (nfnetlink_log)
            8 NONE (nfnetlink_log)
            9 NONE (nfnetlink_log)
           10 ip6t_LOG (ip6t_LOG,nfnetlink_log)
           11 NONE (nfnetlink_log)
           12 NONE (nfnetlink_log)

       The magic numbers (0-12) are Linux address family numbers (AF_INET is 2 and AF_INET6 is
       10).

       The name immediately following the number is the currently-selected backend, and the ones
       in parentheses are the ones that are available. You can change the currently selected
       backend by echoing it's name into /proc/net/netfilter/nf_log.number.

       Example - change the IPv4 backend to LOG:

           sysctl net.netfilter.nf_log.2=ipt_LOG

       Beginning with Shorewall 4.6.4, you can configure the backend using the LOG_BACKEND option
       in shorewall.conf(5)[3] and shorewall6.conf(5)[11].

NOTES

        1. /etc/shorewall/rules
           http://www.shorewall.netmanpages/shorewall-rules.html

        2. data connection associated with an FTP control connection
           http://www.shorewall.netFTP.html

        3. shorewall.conf
           http://www.shorewall.netmanpages/shorewall.conf.html

        4. shorewall-interfaces(5)
           http://www.shorewall.netmanpages/shorewall-interfaces.html

        5. shorewall-policy(5)
           http://www.shorewall.netmanpages/shorewall-policy.html

        6. Shorewall FAQ 16
           http://www.shorewall.netFAQ.htm#faq16

        7. FAQ #17
           http://www.shorewall.net/FAQ.htm#faq17

        8. shorewall.conf(5)
           http://www.shorewall.net/manpages/shorewall.conf.html

        9. shorewall6.conf(5)
           http://www.shorewall.net/manpages6/shorewall6.conf.html

       10. shorewall[6].conf man page
           http://www.shorewall.netshorewall.conf.html

       11. shorewall6.conf(5)
           http://www.shorewall.netmanpages6/shorewall6.conf.html

       12. http://www.shorewall.net/shorewall_logging.html
           http://www.shorewall.net/shorewall_logging.htm