Hello, We would like to use FreeSwitch to test interoperability with our sip registrar platform - as our registrar doesnt handle NAT Traversal we would like to use FS as a mirror proxy . If a call goes through, FS should transparently handle nat traversal functionalities while forwarding the REGISTER/INVITE requests to our registrar server. Below some detailed requirements: Upper Registration is the capability of a SBC to proxy Registrations towards an upstream Registrar. While it is necessary that all SIP requests traverse the SBC for NAT continuity, Registrations should be allowed to be relayed towards our upstream Registrar while the SBC retains a copy of the AOR and masquerade on behalf of the UA that send the registration request. Please let us know the best way to configure FS to achieve this type of configuration. Thank you