L5: A Self Learning Layer 5 Switch

In this paper, we share our experience in designing and building a layer 5 switching system which we call L5. In addition to the layer 2-3-4 information available in the packet, a layer 5 switch uses session level information to route traffic in the network. Session level traffic handling is not a new idea. In fact application level proxies which are functionally equivalent to a layer 5 switch, have been around for years.

Our contribution is in combining the functionalities of an application level proxy with the data handling capabilities of a switch into single system. In this paper, we describe the architecture of the L5 system along with the details of how application level information can be efficiently processed in switch hardware. We cover two specific application examples that we believe are ideal candidates for L5 Switching: one is routing HTTP session based on Uniform Resource Locators (URL) and the other is session-aware dispatching of Secure Socket Layer (SSL) connections.