What is a Flow?

A flow is a stream of packets that has not yet met an expiration criteria, in which the value of a subset of L2, L3, and L4 fields appropriate to the communication exchange are the same for each packet in the stream. ASIC technology implemented on S- and K-Series devices provides for line-rate packet field investigation for the setup and tracking of flows. A flow is unidirectional, and is defined after the first packet is encountered. A network conversation consists of two separate flows, one in each direction. Upon inactivity, a given flow times out after a product-specific timer expires.