- NetBSD Manual Pages
Powered by man-cgi (2021-06-01).
Maintained for NetBSD
by Kimmo Suominen.
Based on man-cgi by Panagiotis Christias.
ipmon - monitors /dev/ipl for logged packets
ipmon [ -abBDFhnpstvxX ] [ -N <device> ] [ -L <facility> ] [ -o [NSI] ]
[ -O [NSI] ] [ -P <pidfile> ] [ -S <device> ] [ -f <device> ] [ <file-
ipmon opens /dev/ipl for reading and awaits data to be saved from the
packet filter. The binary data read from the device is reprinted in
human readable for, however, IP#'s are not mapped back to hostnames,
nor are ports mapped back to service names. The output goes to stan-
dard output by default or a filename, if given on the command line.
Should the -s option be used, output is instead sent to syslogd(8).
Messages sent via syslog have the day, month and year removed from the
message, but the time (including microseconds), as recorded in the log,
is still included.
Messages generated by ipmon consist of whitespace separated fields.
Fields common to all messages are:
1. The date of packet receipt. This is suppressed when the message is
sent to syslog.
2. The time of packet receipt. This is in the form HH:MM:SS.F, for
hours, minutes seconds, and fractions of a second (which can be several
3. The name of the interface the packet was processed on, e.g., we1.
4. The group and rule number of the rule, e.g., @0:17. These can be
viewed with ipfstat -n.
5. The action: p for passed, b for blocked, for a short packet, n did
not match any rules or L for a log rule.
6. The addresses. This is actually three fields: the source address
and port (separated by a comma), the -> symbol, and the destination
address and port. E.g.: 22.214.171.124,80 -> 126.96.36.199,1722.
7. PR followed by the protocol name or number, e.g., PR tcp.
8. len followed by the header length and total length of the packet,
e.g., len 20 40.
If the packet is a TCP packet, there will be an additional field start-
ing with a hyphen followed by letters corresponding to any flags that
were set. See the ipf.conf manual page for a list of letters and their
If the packet is an ICMP packet, there will be two fields at the end,
the first always being `icmp', and the next being the ICMP message and
submessage type, separated by a slash, e.g., icmp 3/3 for a port
In order for ipmon to properly work, the kernel option IPFILTER_LOG
must be turned on in your kernel. Please see options(4) for more
ipmon reopens its log file(s) and rereads its configuration file when
it receives a SIGHUP signal.
-a Open all of the device logfiles for reading log entries from.
All entries are displayed to the same output 'device' (stderr or
-b For rules which log the body of a packet, generate hex output
representing the packet contents after the headers.
Enable logging of the raw, unformatted binary data to the speci-
fied <binarylogfilename> file. This can be read, later, using
ipmon with the -f option.
-D Cause ipmon to turn itself into a daemon. Using subshells or
backgrounding of ipmon is not required to turn it into an orphan
so it can run indefinitely.
specify an alternative device/file from which to read the log
information for normal IP Filter log records.
-F Flush the current packet log buffer. The number of bytes
flushed is displayed, even should the result be zero.
Using this option allows you to change the default syslog facil-
ity that ipmon uses for syslog messages. The default is local0.
-n IP addresses and port numbers will be mapped, where possible,
back into hostnames and service names.
Set the logfile to be opened for reading NAT log records from to
-o Specify which log files to actually read data from. N - NAT
logfile, S - State logfile, I - normal IP Filter logfile. The
-a option is equivalent to using -o NSI.
-O Specify which log files you do not wish to read from. This is
most sensibly used with the -a. Letters available as parameters
to this are the same as for -o.
-p Cause the port number in log messages to always be printed as a
number and never attempt to look it up as from /etc/services,
Write the pid of the ipmon process to a file. By default this
is //etc/opt/ipf/ipmon.pid (Solaris), /var/run/ipmon.pid (44BSD
or later) or /etc/ipmon.pid for all others.
-s Packet information read in will be sent through syslogd rather
than saved to a file. The default facility when compiled and
installed is local0. The following levels are used:
LOG_INFO - packets logged using the "log" keyword as the action
rather than pass or block.
LOG_NOTICE - packets logged which are also passed
LOG_WARNING - packets logged which are also blocked
LOG_ERR - packets which have been logged and which can be con-
Set the logfile to be opened for reading state log records from
-t read the input file/device in a manner akin to tail(1).
-v show tcp window, ack and sequence fields.
-x show the packet data in hex.
-X show the log header record data in hex.
ipmon expects data that it reads to be consistent with how it should be
saved and will abort if it fails an assertion which detects an anomaly
in the recorded data.
ipl(4), ipf(8), ipfstat(8), ipnat(8)
If you find any, please send email to me at firstname.lastname@example.org