IPv6 Media Relay to backend server uses wrong address family

[Finn H]

Hello,

I am attempting to configure flexisip to act as a media relay. I have 
both IPv4 and IPv6 on the client app (Linphone on iOS), Flexisip and the 
upstream SIP server. When I try to make a call from the app, I can hear 
audio from the remote side, but the remote side cannot hear anything 
from the app and eventually the SIP server kills the call due to media 
timeout. During such a call, flexisip logs the following message 
approximately twice a second:

flexisip-warning-Error sending 20 bytes (localport=26459 
dest=2604:a880:2:d0::53c2:1:24935) : Address family not supported by 
protocol

It seems like flexisip is trying to send media using the wrong address 
family. I could be wrong, but it looks like 
https://gitlab.linphone.org/BC/public/flexisip/-/issues/5

That issue hasn't seen any activity in 3 years, is there some kind of 
workaround that I've missed?

Thanks,

--
Finn Herzfeld
Accelerate Networks