Dummynet+Firewall+One_pass question

[Alex de Kruijff]

On Thu, Apr 22, 2004 at 04:25:53PM -0300, Marcelo Pinheiro wrote:
> Hi,
> 
> I am very new to FreeBSD, and I have a quite simple question: How does IPFW
> work when I use PIPES, divert and some other Firewall rules?
> What does net.inet.ip.fw.one_pass mean? For instance, if I use a pipe before
> a divert with one_pass set to 1, the packet passes through the pipe, but
> does not pass through the divert and that makes total sense. However if I
> set one_pass to 1 and set the pipe after the divert using the internal IP
> address ( RFC 1918 ) it works.... that does not make any sense, at least to
> me. :)

man ipfw gives me:
     pipe pipe_nr
             Pass packet to a dummynet(4) ``pipe'' (for bandwidth
limitation, delay, etc.).  See the TRAFFIC SHAPER (DUMMYNET)
CONFIGURATION Section for further information.  The search terminates;
however, on exit from the pipe and if the sysctl(8) variable
net.inet.ip.fw.one_pass is not set, the packet is passed again to the
firewall code starting from the next rule.

> Here are some sample rules:
> 
>         # INTERNAL NETWORK
>         ${fwcmd} pipe 1000 config bw 1024Kbit/s
>         ${fwcmd} pipe 1001 config bw 1024Kbit/s
> 
>         ${fwcmd} add divert natd all from 10.0.0.0/8 to any
>         ${fwcmd} add divert natd all from any to 200.x.x.x
> 
>         ${fwcmd} add pipe 1038 ip from 10.0.0.0/8 to any
>         ${fwcmd} add pipe 1039 ip from any to 10.0.0.0/8
> 
> If I set the way above, it works fine, even if the one_pass is set to 1 (
> one ). The divert changes the packet header to my external IP, and my real
> question is: How in the world the pipe works if the header is changed to
> 200, instead of 10?
> 
> THIS WAY IT DOES NOT WORK WITH ONE_PASS SET TO 1, it passes through the
> pipe, but does not pass through the divert:
> 
>         # INTERNAL NETWORK
>         ${fwcmd} pipe 1000 config bw 1024Kbit/s
>         ${fwcmd} pipe 1001 config bw 1024Kbit/s
> 
>         ${fwcmd} add pipe 1038 ip from 10.0.0.0/8 to any
>         ${fwcmd} add pipe 1039 ip from any to 10.0.0.0/8
> 
>         ${fwcmd} add divert natd all from 10.0.0.0/8 to any
>         ${fwcmd} add divert natd all from any to 200.x.x.x
> 
> I deeply appreciate any ideas.

Thats because the packes that meet the pipe rules are also allowed and
thus never meet the divert rule.

-- 
Alex

Articles based on solutions that I use:
http://www.kruijff.org/alex/index.php?dir=docs/FreeBSD/