The inbound NAT rules create port mapping similar to the port mapping created with load balancer rules. The load balancer rule creates additional settings such as the health probe or session persistence. Inbound NAT rules exclude these settings and create unconditional mapping from the frontend to the backend. Another difference is that the inbound NAT rule forwards traffic directly to a single VM, whereas a load balancer rule forwards traffic to the backend. With the inbound NAT rule, forwarded traffic will always reach the single server in the backend, whereas the load balancer will forward the traffic to the backend pool and it will randomly end in any of the servers in the backend pool.