AsteriskNow external route problem

Hi,
For my school project i have to set up a voip network with 3 types of routes:
– internal
– external
– connection to a voip provider

I’m using AsteriskNOW-1.0.2.1 and to test i use a 3cx softphone software.
The first route(internal) works perfectly.
The second route(external) does’nt work. I can’t connect to the server from outside the network.
My server with the asterisknow installation is directly connected to the dsl internet modem.
I forwarded port 5060. I also fowarded port 3478 for STUN. In my sip.conf i added:

port=5060
bindaddr=0.0.0.0
disallow=all
allow=ulaw
allow=alaw
context=from-sip-external
callerid=Unknown
nat=yes
localnet = 192.168.1.30/255.255.255.0
externip = 2XX.X.XXX.196
fromdomain = 2XX.X.XXX.196
qualify=yes

I used the 3cx debug window to see my error.
I get the following messages:
Attempting to connect 2XX.X.XXX.196
Using network interface 127.0.0.1
Phone got as local port 59086
RTP egine ok
STP engine ok
Sound mic device ok
Sound ring device ok
Phone is sending Stun request
Phone STUN check failed
Phone STUN check failed
Phone STUN check failed
Phone connection failed, server not responding

For STUN i filled in stun01.sipphone.com (a public stun server)

Can anybody assist me with this?

thanks in advance.