The first: Please make sure your port '12345' is opening and then when you using a different network. You have to use the IP address in LAN. Don't use the 'localhost' or '127.0.0.1'. The solution here is: In server
host = '192.168.1.12' #Ip address in LAN network
In client
host = '27.32.123.32' # external IP Address
Hope it works for you