I wanted to have a very simple example of how to setup pf on your freebsd machine and here it it.

First enable pf by adding the following to /etc/rc.conf and rebooting you BSD host to take affect:

pf_enable="YES"  
pf_rules="/etc/pf.conf"  
pflog_enable="YES"  
pflog_logfile="/var/log/pf.log"  

when the machine is back up and running make sure pf is loaded:

moxz:~>kldstat | grep pf  
2 1 0xffffffff81022000 a3c pflog.ko  
3 1 0xffffffff81023000 2bd41 pf.ko  

next create the file /etc/pf.conf and place the following into it:

#Macros  
my_int = "em0"

# Let's just trust localhost  
set skip on lo

# By default, we will block everyone and everything coming in  
block in log all

# accept ssh sessions  
pass in on $my_int proto tcp from any to any port 22 keep state

# accept http sessions  
pass in on $my_int proto tcp from any to any port 80 keep state

# accept icmp sessions  
pass in quick on $my_int proto icmp all keep state

# Outgoing traffic is OK, here we keep state so returning packets  
# are accepted too.  
pass out log proto { tcp, udp, icmp } all keep state  

you can test out your settings by running the following commands:

  • Parse Rules

      pfctl -nf /etc/pf.conf
    
  • Load rules

      pfctl -f /etc/pf.conf
    
  • Watch the logs for blocked packets

      tcpdump -n -e -ttt -i pflog0
    

Published by Karim Elatov

13 May 2011

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