L3 IP based SLB balances all the TCP and UDP traffic from one global virtual IP address to multiple real servers. Unlike L4 SLB, both the virtual service and real service in L3 SLB are defined by single IP address without port number. L3 SLB real services only support ICMP health check. Without specifying port number, L3 SLB works for a much wider range of customers, especially in the following scenarios:
--> Cross-port applications: some session protocols bind multiple connections together, one is the initial connection, others could be generated from dynamic ports
--> Cross-protocol applications: most streaming protocols use UDP connection for data transferring and TCP connection to transfer control information between the same client and server.