Server 2 Server conection kicks in only when needed (user from one server tries to talk to another user on another server, etc.). Both servers have to have distinct domains, e.g. s1.some.local and s2.some.local should work (if domains are the same, then it should be a cluster). In XMPP there is no subdomain distinction (s1 and s2 are different domains, though they are from the same root domain in DNS sense). To test connectivity add both servers to whitelist, open 5269 port, open firewalls, try to ping their names from each other, then try adding a user from another server to conctact list and send a message.