Using 'rdr' on outbound connections

[Brian Candler]

On Thu, Sep 15, 2005 at 01:16:19PM +0100, Greg Hennessy wrote:
> It could do, 
> 
> Make the 1st line of the policy
> 
> block log all 
> 
> 
> And see what it catches. 

/etc/pf.conf now:
rdr pass proto tcp from any to any port 25 -> 127.0.0.1 port 25
rdr pass on lo0 proto tcp from any to any port 25 -> 127.0.0.1 port 25
rdr pass on fxp0 proto tcp from any to any port 25 -> 127.0.0.1 port 25
block log all

Not surprisingly, it blackholes everything.

# telnet -N 147.28.0.39 25
Trying 147.28.0.39...
telnet: connect to address 147.28.0.39: Operation not permitted
telnet: Unable to connect to remote host

# tcpdump -r /var/log/pflog

just shows:

13:26:09.426570 IP bloodhound.noc.clara.net.57393 > rip.psg.com.smtp: S 360892497:360892497(0) win 65535 <mss 1460,nop,nop,sackOK,nop,wscale1,nop,nop,timestamp 9750257 0>

(that's it; no RST, no ICMP ADMIN-PROHIBITED)

I'm coming to the conclusion that 'rdr' acts on an "inbound" interface, i.e.
packets arriving at the kernel, and locally-originated packets don't match
any interface; or something like that.

But I was hoping there would be someone on the list who has a reasonably
deep knowledge of the 'pf' code and could explain whether what I want to do
is not possible, or if it is, how to do it.

Thanks,

Brian.