Newbie IPFW Questions

Glenn Dawson glenn at
Mon Jul 18 03:38:47 GMT 2005

At 08:18 PM 7/17/2005, Jim Campbell wrote:
>I have a machine set up as a classroom to learn about FreeBSD.  It is
>running 4.11 primarily because anything later can't see my hard drive.
>As background, my FBSD machine has an address of  It is
>situated behind a hardware firewall (a Linksys router).  $pif is vr0.
>I'm having problems setting up IPFW to communicate with an Onion router.
>The puzzling part is that I am able to use the Onion router but my
>/var/log/security file says that some of the packets are being dropped.
>Following is what I hope are the pertinent lines from my /etc/ipfw.rules
>$cmd 00225 allow tcp from me to any 9001-9033 out via $pif setup keep-state
>$cmd 00299 deny log all from me to any out via $pif
>$cmd 00332 deny log tcp from any to me established in via $pif
>Next is an excerpt from the /var/log/security file:
>Jul 17 21:49:58 JimsP1G /kernel: ipfw: 299 Deny TCP
> out via vr0
>Jul 17 21:49:59 JimsP1G /kernel: ipfw: 299 Deny TCP
> out via vr0
>Jul 17 21:50:18 JimsP1G /kernel: ipfw: 332 Deny TCP
> in via vr0
>Jul 17 21:50:29 JimsP1G /kernel: ipfw: 332 Deny TCP
> in via vr0
>Now my questions.  First, why isn't rule 225 allowing all the packets out
>to the Onion router?  It seems to me that ipfw should allow all packets
>in the port range 9001-9033 out or none.

Rule 225 will only match packets used to setup the tcp session, once it's 
established you need another rule that will allow the established session 
to function.

Rule 299 is denying everything from leaving your machine except for the 
packets allowed by rule 225.

>Next, the two inbound packets should be returning in response to an 
>outbound packet.  Why are they being dropped?  Are they exceeding some

Rule 332 is denying all established traffic from entering your 
machine.  So, while rule 225 allows you to establish a tcp session with 
another system on ports 9001-9033, once the session is established, rule 
225 no longer applies and rule 332 is then throwing all those packets away.


>Thanks in advance.
>Jim Campbell
>freebsd-questions at mailing list
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