NATed BIND9 with Private IP

Hi Guys,

I am struggelling with a new name server I want to setup.

The Bind9 server is behind a firewall, the firewall is doing natting
(public-private)
It is looks fine.

However when I verify the name server setup from outside my network with
dig @'212.254.246.225' 'kordi.ch' 'soa'
I get a timeout!
dig @'212.254.246.225' 'kordi.ch' 'axfr'
return what I want to see!!

Could it be that I am experiancing problems because my server has a private
ip address and I am using NAT to reach it?

Regards,
Reza Kordi