[Freeswitch-users] Bind Sofia external profile to Static private IP

Hello, Probably an easy thing but my luck I'm stuck in this awkward situation here, I want my sofia external profile to bind to my private IP: 192.168.15.21 , so for the purpose I've edited the vars.xml and sip_profiles/external.xml but still everytime I restart freeswitch it detects the Public IP and binds thye external-sip-ip and external-rtp-ip to the Public IP ? I'm very confused at this and followed all the previous mailing lists threads and to-dos as well but in vain. Waiting for a savior here. -- Thanks Sammy Go.