North-South and East-West Traffic Explained

North-South and East-West Traffic Explained

When you design a network, you want endpoint devices to be able to reach the internet. But, you often need devices inside your network to be able to communicate with each other easily and freely.

Those two ideas form the foundation of north-south and east-west networking traffic. If you take a minute to learn a little more about these concepts, you’ll see how they can help you with network design and security.


Let’s discuss north-south traffic first as it’s very easy to understand and helps inform east-west traffic.

Any communication from a device that is physically located inside the data center has to perform north-south communication to interact with a device that is physically outside of the data center. In other words, when data center devices communicate via the internet, that’s north-south traffic.

Another way to look at it is with a common example. Say you access your cloud account to pull up a document. Assuming you aren’t sitting inside of the data center that runs the cloud tools you’re using, that activity is north-south.


So, if north-south traffic is between a data center and a not-data center, then what does that make east-west traffic?

It’s traffic that originates and terminates all within a single data center. Now, a data center can have a complicated network structure. It can have multiple isolated networks within, and it will certainly have subnetworks. For the sake of east-west traffic, none of that matters. If one device in the data center talks to another device in the same data center, it’s east-west regardless of how convoluted the network might be.

What kind of traffic actually runs east-west? There are a lot of examples. If one server backs up information to another server at the same site, that would constitute east-west traffic. When one switch shares a data table with another, that’s east-west.

Considering how popular virtualization is these days, network devices have to talk to each other a lot to make virtualization possible. So, that’s a huge source of east-west traffic.

Why It Matters

The definitions are pretty straightforward, but how is it useful? Why would you need to distinguish which type of traffic is running through the network?

There are a few reasons, but security tops the list.

Obviously, you need good security measures for north-south traffic. That’s where network attacks and malicious software often come from. But, it’s easy to overlook the importance of security for east-west traffic. It boils down to two things.

First, east-west traffic constitutes a majority of all traffic in a data center, and it’s growing as virtualization and other east-west design ideas and applications grow more popular. So, even if east-west traffic is usually less dangerous, there’s so much of it that you want some level of security.

On top of that, traffic isn’t definitely secure just because it came from within the data center. There are two types of attacks that make this clear. The first is a physical attack. If someone wanted to steal information from an important data center, they might try to physically go to the place and steal things directly. That would involve east-west traffic, and it’s actually how some major data breaches were conducted.

The other concept is even easier to understand. Malicious software can enter a data center through north-south traffic, but once it’s there, it can infect other systems through east-west interactions. If a center gets hit with ransomware, good east-west traffic will mitigate the threat handily.

When you think about networking in these terms, it can help you plan your traffic management well, and most importantly, it can help you avoid classic network security mistakes that could cost you heavily.

Additional Learning Center Resources