STUN server and client

is that install STUN should be must. If we use NATs

There might be no need of stun server if you are going to use it in local all you need is to use local connectivity IP in Linux server and the router when the local ip communication it will start pinging inside the SSH Linux shell if it start pinging then the unreachable issue will be solved or else check the NATing inside the router (option plays better in local connectivity)

I have tried with STUN server. I don’t think it’s a part of this project so you’ll need to use some other open source solution.
However working with stun is a bit of pain in the ass because you’ll need ACS and STUN to work on the same IP address otherwise most clients will not work. If this is possible with your install then you shouldn’t have much problems.