Over the past 3-4 years, the term elephant flows has been used to refer to east-west (machine-to-machine) traffic, such as vMotion, Migration, Backup, and Replication. The term mice flows is used to refer to north-south (user-to-machine) traffic. Why are we using these terms all of a sudden and did they come from?

Wikipedia states “It is not clear who coined “elephant flow”, but the term began occurring in published Internet network research in 2001 when the observations were made that a small number of flows carry the majority of Internet traffic and the remainder consists of a large number of flows that carry very little Internet traffic”.

The traffic that traverses Data Center Interconnects (DCI) is typically east-west and flow-oriented (TCP-based). These applications have huge bandwidth requirements when compared to north-south. RFC 1028 defines a term LFN (Long Fat Network), which is when the Bandwidth Delay Product (BDP) is 10⁵ bits or 12500 bytes. BDP and LFN have existed in the world of WAN Optimization (traditionally for north-south traffic) for over a decade. It is only more recently in the era of east-west traffic in DCI that elephant flows have become more prominent. The terms remain even within a data center, as the folks from VMware have shown in this well-written piece from exactly a year ago.