north-south traffic
also: ingress/egress traffic, border traffic, perimeter traffic
Network traffic that flows between a data center and external networks or the internet, moving vertically across network layers. Contrasts with east-west traffic, which moves between servers within the same data center.
North-south traffic describes data flowing in and out of a data center or network perimeter—the primary path for client-to-server communication. When a user's web browser requests data from a cloud application, that request travels north (into the data center from the internet) and the response travels south (back out). This terminology originated from network diagrams where external networks are traditionally drawn at the top.
Historically, north-south traffic was the dominant flow in enterprise networks. However, modern architectures with microservices, containerization, and distributed systems generate massive amounts of east-west traffic—communication between internal servers and services—which often exceeds north-south volumes.
Example: In a typical web application, user HTTPS requests from the internet represent north-south traffic, while internal requests between your API servers and database servers represent east-west traffic. Network design and security policies must account for both directions appropriately.