[Serusers] Problem with REGISTER

could you please tell me why the following REGISTER request is not getting 401 response..? I am struggling with this problem for the past two days. Kindly update me. REGISTER sip:iptel.org:5060 SIP/2.0 ( if I change sip:iptel.org as sip:195.37.77.101, I am getting 403 response from iptel.org) Via: SIP/2.0/UDP 192.168.14.200:5060;branch=z9hG4bK1436934251 From: san <sip:san@iptel.org>;tag=501424250 To: san <sip:san@iptel.org> Call-ID: 323191517(a)192.168.14.200 <mailto:323191517@192.168.14.200> CSeq: 1 REGISTER Contact: san <sip:san@192.168.14.200:5060> max-forwards: 50 user-agent: oSIP-ua/0.8.1 expires: 3600 Content-Length: 0 Thankyou Santhosh.S