firewall dynamic IP

[Antoine Jacoutot]

Hi !

In my progress of still learning firewall with ipfw, I have a question.
Can I convert the following rule:

${fwcmd} add pass tcp from any to ${oip} 25 setup

into on of those (which one would be the best, I guess the second one, right 
?):

${fwcmd} add pass tcp from any to any via tun0 25 setup
${fwcmd} add pass tcp from any to me in via tun0 setup

I ask this question because I do not have a fixed @ip on the outside interface 
so I cannot use the ${oip} (outside @ip) variable.

By the way, is there a difference between:
${fwcmd} add pass... and ${fwcmd} add allow... ?

Thanks in advance for your answers.

Antoine