In order to log packets passing through PF, the log keyword must be used. The log keyword causes all packets that match the rule to be logged. In the case where the rule is creating state, only the first packet seen (the one that causes the state to be created) will be logged.
The options that can be given to the log keyword are:
Options are given in parenthesis after the log keyword; multiple options can be separated by a comma or space.
pass in log (all, to pflog1) on $ext_if inet proto tcp to $ext_if port 22 keep state
To view the log file:
# tcpdump -n -e -ttt -r /var/log/pflog
Note that using tcpdump(8) to watch the pflog file does not give a real-time display. A real-time display of logged packets is achieved by using the pflog0 interface:
# tcpdump -n -e -ttt -i pflog0
NOTE: When examining the logs, special care should be taken with tcpdump's verbose protocol decoding (activated via the -v command line option). Tcpdump's protocol decoders do not have a perfect security history. At least in theory, a delayed attack could be possible via the partial packet payloads recorded by the logging device. It is recommended practice to move the log files off of the firewall machine before examining them in this way.
Additional care should also be taken to secure access to the logs. By default, pflogd will record 160 bytes of the packet in the log file. Access to the logs could provide partial access to sensitive packet payloads (like telnet(1) or ftp(1) usernames and passwords).
# tcpdump -n -e -ttt -r /var/log/pflog port 80
This can be further refined by limiting the display of packets to a certain host and port combination:
# tcpdump -n -e -ttt -r /var/log/pflog port 80 and host 192.168.1.3
The same idea can be applied when reading from the pflog0 interface:
# tcpdump -n -e -ttt -i pflog0 host 192.168.4.2
Note that this has no impact on which packets are logged to the pflogd log file; the above commands only display packets as they are being logged.
In addition to using the standard tcpdump(8) filter rules, the tcpdump filter language has been extended for reading pflogd output:
# tcpdump -n -e -ttt -i pflog0 inbound and action block and on wi0
This display the log, in real-time, of inbound packets that were blocked on the wi0 interface.
Create the following script:
#!/bin/sh PFLOG=/var/log/pflog FILE=/var/log/pflog5min.$(date "+%Y%m%d%H%M") pkill -ALRM -u root -U root -t - -x pflogd if [ -r $PFLOG ] && [ $(stat -f %z $PFLOG) -gt 24 ]; then mv $PFLOG $FILE pkill -HUP -u root -U root -t - -x pflogd tcpdump -n -e -s 160 -ttt -r $FILE | logger -t pf -p local0.info rm $FILE fi
Edit root's cron job:
# crontab -u root -e
Add the following two lines:
# rotate pf log file every 5 minutes
0-59/5 * * * * /bin/sh /etc/pflogrotate
Add the following line to /etc/syslog.conf:
If you also want to log to a remote log server, add the line:
Make sure host syslogger has been defined in the hosts(5) file.
Create the file /var/log/pflog.txt to allow syslog to log to that file, and give it the same permissions as the pflog file.
# touch /var/log/pflog.txt
# chmod 600 /var/log/pflog.txt
Make syslogd notice the changes by restarting it:
# kill -HUP $(cat /var/run/syslog.pid)
All logged packets are now sent to /var/log/pflog.txt. If the second line is added they are sent to the remote logging host syslogger as well.
The script /etc/pflogrotate now processes and then deletes /var/log/pflog so rotation of pflog by newsyslog(8) is no longer necessary and should be disabled. However, /var/log/pflog.txt replaces /var/log/pflog and rotation of it should be activated. Change /etc/newsyslog.conf as follows:
#/var/log/pflog 600 3 250 * ZB "pkill -HUP -u root -U root -t - -x pflogd" /var/log/pflog.txt 600 7 * 24
PF will now log in ASCII to /var/log/pflog.txt. If so configured in /etc/syslog.conf, it will also log to a remote server. The logging is not immediate but it can take up to about 5-6 minutes (the cron job interval) before the logged packets appear in the file.