In context of networking I keep running into statements such as "east-west traffic is larger than north-south traffic". I have tried a bit of googling but have not been able to locate an authoritative answer to understand the origin of these terms.

  • What is the definition of north-south traffic?
  • What is the definition of east-west traffic?
  • What is the origin of these terms?
up vote 31 down vote accepted

The terms are usually used in the context of data centers.

Generally speaking, "east-west" traffic refers to traffic within a data center -- i.e. server to server traffic. "North-south" traffic is client to server traffic, between the data center and the rest of the network (anything outside the data center).

I believe the terms have come into use from the way network diagrams are typically drawn, with servers or access switches spread out horizontally, and external connections at the top or bottom.

  • They probably share origins with optical networking as well. – John Jensen Jun 1 '15 at 16:18

It has also been, in my years of understanding, general network traffic descriptors:

North/South - Meaning traffic coming into and out of the network into Internet space, i.e in and out of edge firewalls and/routers.

East/West - Traffic internal to the network that doesn't leave, i.e. LAN client to server and server to server communications.

North South traffic is usually considered from end users to the internet, where traditionally organizations used to have fat links to end user and thin links to the external connectivity. In the recent times, the traffic patterns have changed drastically and more traffic is generated inside the data center in a server to server communication which is referred as east west traffic.

I have also seen it used in an NFV context where the traffic entering/leaving a NFV stack. North/South (entering and leaving a virtual router) and traffic between modules at the same layer in the same physical infrastructure is referred to as East/West, i.e. Routing within the same physical box.

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