Section: Maintenance Commands (8)Updated: 25 April 2004Local indexUp
fwlogwatch - a firewall log analyzer and realtime response agent
produces Linux ipchains, Linux netfilter/iptables, Solaris/BSD/Irix/HP-UX
ipfilter, ipfw, Cisco IOS, Cisco PIX/ASA, NetScreen, Elsa Lancom router and
Snort IDS log summary reports in plain text and HTML form and has a lot of
options to analyze and display relevant patterns. It also can run as daemon
(with web interface) doing realtime log monitoring and reporting anomalies
or starting attack countermeasures.
These options are independent from the main modes of operation.
Show the available options.
Show time of the first and the last log entry. The input file(s)
can be compressed or plain log file(s). Summary mode will show the
time of the first and last packet log entry, this log times mode
will show the time of the first and last entry overall.
Show version and copyright information and the options used to compile
The global options for all modes are:
Show the amount of data in bytes this entry represents, this is the sum of
total packet lengths of packets matching this rule (obviously only available
for log formats that contain this information).
Use the alternate configuration file
instead of the default configuration file
(which does not need to exist). Only options not specified in the files can
be overridden by command line options.
Do not differentiate destination IP addresses. Useful for finding scans in
Differentiate destination ports.
Specific hosts, ports, chains and branches (targets) can be selected or
excluded, selections an exclusions can be added and combined. The
is composed of one of the functions
exclude, then one of the parameters
branch. In case of a host or port a third parameter for
destination is needed. Finally, the object is directly appended, in case of
a host this is an IP address (networks can be specified in CIDR format),
port is a number and chain and branch are strings. To show entries with
destination port 25 you would use
and to exclude entries which have the class C network 192.168.1.0 as source
or belong to the chain INPUT:
If you only want to see a fixed maximum amount of entries (e.g. the "top 20")
this option will trim the output for you.
When analyzing large amounts of data you usually aren't interested in entries
that have a small count. You can hide entries below a certain threshold with
Enable service lookups. Port numbers will be looked up in /etc/services.
Enable DNS lookups. Host names will be resolved (reverse and forward lookup
with a warning if they don't match). This makes summary generation very
slow if a lot of different hosts appear in the log file. Resolved host names
This is the sort order of the summary and packet cache. Since entries often
are equal in certain fields you can sort by several fields one after another
(the sort algorithm is stable, so equal entries will remain sorted in the
order they were sorted before). The sort string can be composed of up to 11
fields of the form
is the sort criteria:
byte count (sum of total packet lengths),
destination host and
is the direction:
Sorting is done in the order specified, so the last option is the primary
criteria. The default in summary mode is
(start with the highest count, if two counts match list the one earlier in
time first) of which
is built in, so if you specify an empty sort string or everything else is
equal entries will be sorted ascending by time. The realtime response mode
is not built in).
Only use certain parsers, where the log
can be one or a combination of:
Elsa Lancom and
Snort. The default is to use all parsers except the ones for NetScreen,
Elsa Lancom and Snort logs.
Differentiate protocols. This is activated automatically if you
differentiate source and/or destination ports.
Differentiate source ports.
as title of the report and status page.
Be verbose. You can specify it twice for more information.
In very verbose mode while parsing the log file you will see "." for
relevant packet filter log entries, "r" for 'last message repeated' entries
concerning packet filter logs, "o" for packet filter log entries that are
too old and "_" for entries that are not packet filter logs.
Differentiate TCP options. All packets with a SYN are listed separately,
other TCP flags are shown in full format if they are available (ipchains
does not log them, netfilter and ipfilter do, Cisco IOS doesn't even log SYNs).
LOG SUMMARY MODE
This are additional options that are only available in log summary mode:
Show timestamp of last packet logged. End times are only available if
there is more than one packet log entry with unique characteristics.
Process recent events only. See
below for the time options.
Specify an output file.
Do not differentiate source IP addresses.
The summary will be sent by email to this address. If HTML output is
selected the report will be embedded as attachment so HTML-aware mail
clients can show it directly.
Show timestamp of first packet logged.
Look up information about the source addresses in the whois database. This
is slow, please don't stress the registry with too many queries.
Produce output in HTML format.
Show time interval between start and end time of packet log entries. This
is only available if there is more than one packet log entry with unique
REALTIME RESPONSE MODE
Enter realtime response mode. This means: detach and run as daemon until
the TERM signal (kill) is received. The HUP signal forces a reload of the
configuration file, the USR1 signal forces fwlogwatch to reopen and read the
input file from the beginning (useful e.g. for log rotation). All output
can be followed in the system log.
Alert threshold. Notify or start countermeasures if this limit is reached.
Defaults to 5.
Forget events that happened this long ago (defaults to 1 day). See
below for the time options.
This option defines a host or network in CIDR notation that will never be
blocked or other actions taken against. To specify more than one, use the
-k parameter again for each IP address or network you want to add.
The notification script is invoked when the threshold is reached. A few
examples of possible notifications are included in fwlw_notify, you can add
your own ones as you see fit.
The response script is invoked when the threshold is reached. Using the
example script fwlw_respond this will block the attacking host with a new
firewall rule. A new chain for
actions is inserted in the input chain and block rules added as needed.
The chain and its content is removed if
is terminated normally. The example scripts contain actions for ipchains
and netfilter, you can modify them or add others as you like.
Activate the internal web server to monitor and control the current status
of the daemon. It listens on the specified
and by default only allows connections from localhost. The default user
and the default password is
(since DES can only encrypt 8 characters). All options related to the
status web server can be changed in the configuration file.
You can specify one or more input files (if none is given it defaults to
). Relevant entries are automatically detected so combined log files (e.g.
from a log host) are no problem. Compressed files are supported (except in
realtime response mode where they don't make sense anyway). The '-' sign
may be used for reading from standard input (stdin). In realtime response
mode the file needs to be specified with an absolute path since the daemon
uses the file system root (/) as working directory.
Time is specified as
is a natural number and
is one of the
for seconds (this is the default),
for months and
Default configuration file.
Default input log file.
Default PID file generated by the daemon in realtime response mode if
configured to do so.
FEATURES ONLY IN CONFIGURATION FILE
The following features are only available in the configuration file and not
on the command line, they are presented and explained in more detail in the
sample configuration file.
HTML colors and stylesheet
The colors of the HTML output and status page can be customized, an
external cascading stylesheet can be referenced.
Realtime response options
Verification of ipchains rules, PID file handling, the user
should run as, the location of the notification and response scripts, which
address the status web server listens on, which host can connect, the
refresh interval of the status page and the admin name and password can be
is a security tool special care was taken to make it secure. You can and
should run it with user permissions for most functions, you can make it
setgid for a group
is in if all you need is to be able to read this file. Only the realtime
response mode with activated ipchains rule analysis needs superuser
permissions but you might also need them to write the PID file, for actions
in the response script and for binding the default status port. However, you
can configure fwlogwatch to drop root privileges as soon as possible after
allocating these resources (the notification and response scripts will still
be executed with user privileges and log rotation might not work).