Juniper Zones Explained

Usually hovering around 10% of the router market share, Juniper Networks might not have a global stranglehold on networking products, but they're also not negligible. For top-of-the-line speed, throughput, and open architecture, Juniper outperforms its competition — including Cisco, which holds a larger, broader market share.

Juniper networks are particular, though, from their hardware to their security. Juniper's best approaches to security include the Juniper Networks SRX Series Gateways—high-performance enterprise security, routing, and networking devices. Understanding Juniper zones is key to understanding how SRX gateways keep the right people in and the wrong people out.

What is a Juniper Security Zone?

Quick Definition: Network traffic has to have a place to enter and exist on network devices — those are interfaces. In Juniper networks, a security zone is what you get when interfaces get bundled together and given the same regulation requirements. A zone is a group of interfaces with similar security needs.

An Overview of Juniper Zones [VIDEO]

In this video, Scott Morris covers Juniper zone concepts and their interaction with the security gateway in JUNOS (SRX). Simply put, a zone is a group of interfaces with similar security needs, and policies will handle how traffic is controlled between these zones.

How Do Juniper Security Zones Work?

In this post, we'll explore Juniper security zones and how they're defined and operate. Consider this a preliminary introduction to the idea of Junos zones, not a definitive tutorial on managing and configuring Junos security. For more in-depth training in Juniper configuring, browse CBT Nuggets' training for Juniper Networks.

The easiest way to imagine zones is to conceptualize a hypothetical network diagram. On one side of our network, we have the wide, open Internet, and separating our network from the hazards and dangers of the web is a Juniper SRX device. The SRX is connected to four EX4200s, a Juniper ethernet switch through four separate interfaces.

Those four EX4200s each belong to a zone. Because the interfaces inside each zone receive identical security regulations, it's pretty standard to separate zones according to functional departments. So, in our case, we'll have an IT Zone for our IT staff and department, a Data Center Zone, an Engineering Zone, and a Human Resources Zone. Depending on the organization's size, we might also have many other zones.

In our network diagram, the Internet is separated from our network, but the most accurate way to conceptualize the Internet in this case would be to call it the Internet Zone. All the traffic in the Internet Zone is separated from our internal zones by routers and switches. The network engineer's job is to set up the interfaces to belong to one zone or another.

What is the Null Zone in Juniper Network Security?

In Juniper Network Security, there is a Null Zone or "blank" zone. The Null Zone exists by default, and all interfaces that aren't assigned anywhere else belong to it. What's essentially happening in the Null Zone is that all traffic going into and out of that zone is getting dropped. The default behavior of the Null Zone is that it doesn't go anywhere.

Once you know this about the Null Zone, it's a standard security practice. But if you're unfamiliar with this default behavior, it can be confusing and annoying. Because out of the box, if you plug in an SRX device, you'll find that network traffic isn't routing. The traffic doesn't get where you want it to, and you likely wouldn't know why. On Juniper devices, interfaces are in the null zone by default, where traffic won't be passed until the interface is assigned to a zone.

There are some minor exceptions to this. Management interfaces like fxp0 and em0 don't technically start in the null zone. Nevertheless, fxp0 and em0 interfaces—acting like standard management interfaces—allow network access to each node in the cluster and still need to be configured before being accessed.

Juniper Security Zone Rules vs. Juniper Security Zone Policies

Something to remember about zones is that management interfaces like fxp0 and em0 don't need to be explicitly attached to a zone because zones define transit rules. That is, zones regulate packets coming in or out of the router itself. Zones focus on the transit and egress of packets from and between users.

There are rules about zone behavior, too. But by that, we don't mean policies. Zone policies are the rules for handling traffic. Zone rules are how zones behave, what they're capable of, and, most importantly, what they're not capable of.

Zones exist to have logical interfaces assigned to them. A logical interface may be assigned to a zone, but it can't be transferred to more than one zone. Similarly, a logical interface can be assigned to a routing instance. But you can't assign the same logical interface to multiple routing instances. In both zones and routing instances, it's got to be one thing or another.

To think back to our network diagram, we couldn't have a single interface in both HR and Engineering. We might set up access controls that allow for highly similar features between the HR and Engineering interfaces, but we can't have one interface belong to multiple zones.

Notice that we're referring to the point on the device that does the routing as the "logical interface." That term might throw you off if you're unfamiliar with routing in the Junos world. But you might have heard it referred to elsewhere as a unit in another routing schema. Other vendors also refer to the concept as a "sub-interface." Whatever you want to call it is fine.

But it's important to understand that the logical portion must belong to one and only one zone or routing instance. Abstracting the interface and converting it to a logical interface for the SRX to interact with means that it can't be subdivided into other zones and interfaces.

Can Logical Interfaces in the Same Zone Be Assigned to Different Routing Interfaces?

No, a logical interface cannot be assigned to routing interfaces that are different from others in the same zone. This is due to the interfaces' logical abstraction.

In other words, we can't have some places in HR that belong to one routing instance and others that belong to another. Remember that a zone is a group of interfaces receiving the same security measures and transit policies. Splitting a zone up in that way wouldn't just be counterintuitive; it would make for a freakishly confusing situation on the SRX itself.

The bottom line regarding zone behavior is that if you want to assign different interfaces in the same zone to different routing interfaces, you'll need to set up multiple zones. This means that an incredibly important part of planning and creating your zones is understanding and taking into account how your interfaces are done. All logical interfaces in one particular zone must belong to the same routing instance.

To that effect, many engineers keep the demarcation very simple. In other vendors, you might see the simple differentiation of "Inside" and "Outside." In the Juno world, that isn't quite the default behavior. The default behavior on branch devices will have some zones already baked in. Those are typically a "Trust" and an "Untrust".

Wrapping Up

The common wisdom in the IT world is that Juniper Networks' relatively small market share tends to mean that the IT professionals who are trained and familiar with the devices are especially valuable. It's a matter of low supply and considerable demand.

Understanding Juniper zones, how they route, and the rules that govern them is core to using and securing Juniper networks. If you're interested in starting a career in Junos networking, consider CBT Nuggets' associate-level JNCIA-Junos training.