Understanding ownership and authority

By default, Netcode for GameObjects assumes a client-server topology, in which the server owns all NetworkObjects (with some exceptions) and has ultimate authority over spawning and despawning.

Checking for authority

IsServer

IsServer or !IsServer is the traditional client-server method of checking whether the current context has authority.

public class MonsterAI : NetworkBehaviour
{
    public override void OnNetworkSpawn()
    {
        if (!IsServer)
        {
            return;
        }
        // Server-side monster init script here
        base.OnNetworkSpawn();
    }

    private void Update()
    {
        if (!IsSpawned || !IsServer)
        {
            return;
        }
        // Server-side updates monster AI here
    }
}