Layer 4 Switching
Layer 4 switching is considered a hardware-based layer 3 switching technology that can also consider the application used (for example, Telnet or FTP).
Layer 4 switching provides additional routing above layer 3 by using the port numbers found in the Transport layer header to make routing decisions.
These port numbers are found in Request for Comments (RFC) 1700 and reference the upper-layer protocol, program, or application.
Layer 4 information has been used to help make routing decisions for quite a while. For example, extended access lists can filter packets based on layer 4 port numbers. Another example is accounting information gathered by open standards using sFlow provided by companies like Arista Networks or proprietary solutions like NetFlow switching in Cisco's higher-end routers.
The largest benefit of layer 4 switching is that the network administrator can configure a layer 4 switch to prioritize data traffic by application, which means a QoS can be defined for each user.
For example, a number of users can be defined as a Video group and be assigned more priority, or band-width, based on the need for video conferencing.
Read more about this topic: LAN Switching
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