im having my FS box behind NAT, the network topology is something like:

IP PHONE A(Public IP)<------->NAT<------>FS(Private IP, with a public IP)<------->IP PHONE B(Private IP)

i was trying to have IP PHONE B able to make call to IP PHONE A and have two-way talk.

with the default FS configuration when IP PHONE B calls IP PHONE A, there's only one-way talk, A can hear B but B cannot hear A.

then i decided to use stun by modifying:

vars.xml

<X-PRE-PROCESS cmd="set" data="external_rtp_ip=stun:stun.freeswitch.org"/>  // this is the default config

<X-PRE-PROCESS cmd="set" data="external_sip_ip=stun:stun.freeswitch.org"/>  // this is the default config

internal.xml

<param name="ext-rtp-ip" value="stun:stun.freeswtich.org"/>

<param name="ext-sip-ip" value="stun:stun.freeswtich.org"/>

external.xml

<param name="ext-rtp-ip" value="stun:stun.freeswtich.org"/>

<param name="ext-sip-ip" value="stun:stun.freeswtich.org"/>

but while restarting FS, there's error reporting:

2013-08-08 10:33:58.933096 [ERR] sofia_glue.c:1043 STUN Failed! stun.freeswitch.org:3478 [Bind Error!]

2013-08-08 10:33:58.933096 [ERR] sofia.c:4074 Failed to get external ip.

2013-08-08 10:33:58.934072 [NOTICE] sofia.c:4754 Started Profile external [sofia_reg_external]

...

2013-08-08 10:34:00.859927 [ERR] sofia_glue.c:1043 STUN Failed! stun.freeswitch.org:3478 [Bind Error!]

2013-08-08 10:34:00.859927 [ERR] sofia.c:4074 Failed to get external ip.

2013-08-08 10:34:00.860904 [NOTICE] sofia.c:4754 Started Profile internal [sofia_reg_internal]

so am i still missing some configuration or anything else was wrong?