[asterisk-users] one way RTP using NAT

[Hector Quiroz]

Hi,
I'm having a problem with my asterisk, trying to connect to a CISCO 2840 IOS12.x
ASterisk is behind firewall NATing, when it do the handshaking for
RTP, it sends his internal IP instead of sending the external one.
How can I tell the asterisk box, to modify that and send the external IP?
I tryied with Sip.conf's externip=xxxx and localnet=xxxx, nat=yes
Nothing seems to change the contact field on SIP protocol going out
from the asterisk box..

thanks.
Hector.