IPFWPCAP(8) MidnightBSD System Manager’s Manual IPFWPCAP(8)


ipfwpcap — copy diverted packets to a file in tcpdump format


ipfwpcap [−dr] [−b maxbytes] [−p maxpkts] [−P pidfile] portnum dumpfile


The ipfwpcap utility is used to copy diverted packets to a file in tcpdump(1) format. The interesting packets are diverted by ipfw(8) to a port on which ipfwpcap listens. The packets are then dropped unless −r is used.

The options are as follows:


Turns on extra debugging messages.


Writes packets back to the divert(4) socket.


Indicates that it is okay to quit if maxbytes or maxpkts are reached. Diverted packets will silently disappear if nothing is listening on the divert(4) socket.

−b maxbytes

Stop dumping after maxbytes bytes.

−p maxpkts

Stop dumping after maxpkt packets.

−P pidfile

File to store PID number in. Default is /var/run/ipwfpcap.portnr.pid.

The portnum argument specifies which divert(4) socket port to listen on. The dumpfile argument is the path to the file to write captured packets to. Specify ‘’ to write to stdout.


The ipfwpcap utility exits 0 on success, and >0 if an error occurs.


ipfwpcap -r 8091 divt.log &

Starts ipfwpcap as a background job listening to port 8091 and reflecting the packets back to the socket.

ipfw add 2864 divert 8091 ip from

Example ipfw(8) rule to divert all packets from to port 8091. See ipfw(8) for details.


tcpdump(1), pcap(3), divert(4), ipfw(8)


The ipfwpcap utility first appeared in FreeBSD 7.0.


ipfwpcap was written by P. Kern 〈pkern@cns.utoronto.ca〉. This manual page was written by Niclas Zeising 〈niclas.zeising@gmail.com〉.

MidnightBSD 0.3 May 22, 2006 MidnightBSD 0.3