Asterisk NAT unable to hear voice (outgoing call)

Dear All,

My asterisk (asterisk 1.8.6) + FreePBX 2.9.0.7 is located behind firewall
I have natted the following ports:


in my /etc/sysconfig/iptables

-A INPUT -p tcp -m tcp --dport 5060 -j ACCEPT
-A INPUT -p udp -m udp --dport 5060 -j ACCEPT
-A INPUT -p udp -m udp --dport 4569 -j ACCEPT
-A INPUT -p udp -m udp --dport 10001:20000 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 5038 -j ACCEPT

-A NAT -p tcp -m tcp -d 202.a.b.c/32 -i eth3 --dport 5060 -j DNAT --to-destination 172.a.b.c:5060
-A NAT -p udp -m udp -d 202.a.b.c/32 -i eth3 --dport 5060 -j DNAT --to-destination 172.a.b.c:5060
-A NAT -p udp -m udp -d 202.a.b.c/32 -i eth3 --dport 10001:20000 -j DNAT --to-destination 172.a.b.c:10001-20000
-A NAT -p udp -m udp -d 202.a.b.c/32 -i eth3 --dport 4569 -j DNAT --to-destination 172.a.b.c:4569
-A NAT -p tcp -m tcp -d 202.a.b.c/32 -i eth3 --dport 5038 -j DNAT --to-destination 172.a.b.c:5038

in my /etc/asterisk/rtp.conf
rtpstart=10001
rtpend=20000

and my /etc/asterisk/sip_general_additional.conf is:

callevents=no
jbenable=no
rtptimeout=30
maxexpiry=3600
allowguest=yes
defaultexpiry=120
minexpiry=60
srvlookup=no
registerattempts=0
registertimeout=20
g726nonstandard=no
t38pt_udptl=no
videosupport=no
maxcallbitrate=384
canreinvite=no
notifyhold=yes
notifyringing=yes
checkmwi=10
rtpkeepalive=0
rtpholdtimeout=300
nat=yes
externip=202.a.b.c
localnet=172.a.b.0/255.255.255.0
[[email protected] asterisk]# netstat -tunap |grep asterisk
tcp        0      0 0.0.0.0:5038                0.0.0.0:*                   LISTEN      2786/asterisk
tcp        0      0 127.0.0.1:5038              127.0.0.1:50243             ESTABLISHED 2786/asterisk
udp        0      0 0.0.0.0:5060                0.0.0.0:*                               2786/asterisk
udp        0      0 0.0.0.0:4569                0.0.0.0:*                               2786/asterisk
[[email protected] asterisk]#

is there anything else I missed?

why, I am unable to hear the voice of someone I called

please help

thanks & Regards
Winanjaya