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