The Basics of Networking in Unreal Engine 5
When you first dive into Unreal Engine multiplayer, the word networking might sound intimidating. But really, it’s just about computers talking to each other, sending and receiving data.
Let’s break it down in plain language:
What is Networking?
At its core, networking in games means sending data between computers. That can cover a lot of ground, like:
Player accounts (username, rank, in-game currency, etc.)
Messaging and voice chat
Multiplayer gameplay (syncing properties, functions, actions)
Basically, anything that lets players interact in the same shared world.
How Does the Connection Work?
There are two main players in the networking game:
Client → This is the actual game running on your PC or console. It takes your input (keyboard, controller, etc.) and shows you visuals + sounds.
Server → The boss. It’s authoritative. Whatever happens on the server is the “truth,” and those changes get replicated to clients. The server doesn’t care about visuals (it’s just data).
What Runs Only on a Client?
Not everything needs to be handled by the server. Some things live happily on the client side:
Widgets (UI)
VFX, animations, IK
Local prediction for lag compensation (like moving or shooting when there’s delay)
Local physics (including ragdolls, destruction*)
*Fun fact: some modern games—like The Finals—push more physics to the server for accuracy.
Replication Is The Core Functionality Networking
Replication is Unreal’s way of making sure everyone sees the same thing. It synchronizes processes between machines so your “grenade explosion” shows up for everyone, not just you.
Net Modes: Listen vs Dedicated Servers
Listen Server → One of the players also acts as the server. It’s cheaper but needs good internet + strong hardware.
Dedicated Server → A standalone build of the game that only handles networking. No visuals, no player input, just pure server power. This is what most big games use.
How Replication Works in Practice
Every connection has channels reserved for replicated actors.
You can:
Enable replication on an Actor (set its “replicates” flag to true).
Replicate a UActorComponent (inherits replication from parent class).
Control who gets to see updates with relevancy settings (replicate to all, or just to the owner).
Types of Replication
Lifetime Replication
Spawned on the server → exists on clients.
Destroyed on the server → gone on clients.
Replicated Properties
Server changes variables → clients receive updates automatically.
RepNotify is super useful, it triggers a function when a variable updates on a client.
Remote Procedural Calls (RPCs)
Server RPC: Called on client → runs on server.
Client RPC: Called on server → runs on one client.
Multicast RPC: Called on server → runs on all clients (but only if the Actor is relevant).
Ownership and Relevancey
Actors can “own” other actors.
Example: PlayerState → Pawn → Weapon.
Ownership matters because it determines who gets updates.
Relevancy decides whether an Actor’s data should be sent to everyone, or just specific players (like only the owner).
Example: Replication in Action
Let’s say we have a variable called PlayerLobbyInfo.
It exists on the server and the client.
When it changes, best practice is:
Update it on the server.
Let replication push it down to the clients.
Use RepNotify to trigger UI updates.
That way, no one cheats the system and everyone stays in sync.
Key Native Classes & Replication
Some classes in Unreal already have replication built in:
Player Controller
Player State
Game State
Game Mode
Conclusion Points
Networking in Unreal boils down to a few essentials:
Clients handle input and display.
Servers keep authority and push updates.
Replication keeps everything consistent.
Ownership and relevancy decide who gets what data.
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