I get that a dedicated server is likely created so anyone in the world can generally join the game. Listen servers are more local. But are there any problems with using only listen servers for an MMO game?
Besides he fact that it has one extra player because they spawn with the creation of the server?
Problem is that the player is the Server and he can technily cheat very easily. Basicly you give Client Authority over the Game and every Problem that comes with it. Advantage is that you don´t have to run any Server Infrastructure since anyone can create a Server where others can Join (also globaly you only need a IP to connect)
I assume you talk about classic MMOs like WoW, Guild Wars and that sort that have a certain Persistance Layer, account Management, Ranking Systems, etc. thats something you dont want to give into Client Hands ever =)
There is also what you can call a Hybrid. You got Listen Servers that can do Request to global Servers but never directly access or Modify Data on that global Server. But its often Hard to verify the Data that comes from the listen Server since the global one does not know much about what actually happens ingame.
Do a bit of research its covered somewhat well across the Internet.
Nope one Client is the Server! Thats the big difference. And he can execute Server functionality aswell as reverse engineer sensitive Data. Or simply change Data thats sitting in Memory directly. You can simply say the server is on his Machine and he can Manipulate it.
On a Dedicated server no Player has any direct access since everyone just connects to the Server. Nobody owns it. It makes it also harder to hack if someone sends some shady package the server can verify it. Did not happen on the Server → refuse the package.
And all those nodes you mentioned are executed by the Client since he is the Server. He runs all the Functions and tells other Clients whats going on. See the Problem now? ^^
So how would you go about executing Server functionality, or accessing sensitive Data?
Does it happen outside of the game? Through the console? Shipping packages don’t allow the console…
There are planty of tools out there like Disasamblers, Cheat Engine, Code injection, etc. its data on your PC you can manipulate (Edit) it if you got the skills (and planty of people out there got those skills) you don´t need a UE4 console for that 