IPv6 Media Relay to backend server uses wrong address family
When you configure flexisip as a frontend proxy server for a ipv6 only backend server using domain names only, flexisip does the following (versus the backend server):
local=[185.x.y.z|28920:28921] remote=[fd12:xx:yy:zz:aa|34096:34097]
where remote is in fact the address of the backend server.
As far as I was able to track it down (I do not have a buildsystem up and running) I think it is because if a INVITE is sent from the voip client via flexisip to the backend in the form extension@domain-name-not-ip.com, Agent::getPreferredIp() gets the domain name and not the actual ip address of the backend. In that case getPreferredIp() will always select IPv4