[SR-Users] Change of source ip address

Dear list, I'm having a problem. I have an SBC server with two network interfaces, one external IP (X.X.248.194) and other internal IP (X.X.248.21). Messages are sent to the proxy sip server through internal ip with this configuration: route [sip-serverr] { rewritehostport ("ip_sip_proxy: 5060"); force_send_socket (X.X.248.21: 5060); t_relay (); exit; } When a UA sends an INVITE to the SBC, the responses (back) to UA are being sent with the correct external source IP (X.X.248.194) but if there are retransmissions of these responses, after 6 seconds, the source IP changes to the internal ip (X.X.248.21) Does anyone from the list know how I can solve this? Attached picture of wireshark capture for better understanding. -- Diego Alejandro Ozuna