east-west traffic
also: internal traffic, lateral traffic, intra-data center traffic
Network traffic that flows between servers within the same data center or internal network, as opposed to traffic entering or leaving the network (north-south). It refers to the horizontal movement of data between compute, storage, and other infrastructure resources.
East-west traffic is the dominant type of communication in modern data center architectures, flowing laterally between internal systems rather than vertically through perimeter gateways. In a traditional three-tier application, this includes database-to-application server communication, cache server queries, and service-to-service interactions within microservices architectures.
The term contrasts with north-south traffic, which represents data entering from or exiting to external networks (clients, the internet, remote offices). For example, a user request is north-south, but the internal queries your application makes to three different backend services to fulfill that request are east-west.
Understanding east-west traffic is critical for security, performance, and network design. Organizations use internal firewalls, service meshes, and zero-trust security models to monitor and control this traffic, since the majority of modern application communication happens internally rather than across network boundaries.