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Junos® OS For Dummies®, 2nd Edition by Michael Bushong, Cathy Gadecki, Walter Goralski

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Taking a Peek Inside the Junos OS

How engineers design a network operating system impacts the reliability, security, scalability and performance of not just the devices, but also the overall network, particularly in large-scale systems. The operating system must handle the many different processes essential to running today's global networks, while also assuring fair sharing of resources so that no process or service can starve out others.

World-class architecture

The architecture of the Junos operating system cleanly divides the functions of control, services, and forwarding into different planes. The control and services planes include many different processes that run in different modules of the operating system. The explicit division of responsibility allows the software to run on different engines of processing, memory, and other resources. This division of labor is what enables Junos to run all types of platforms in all matter of sizes, from a small box in a home office to the largest boxes in the world handling terabits of data every second.

Figure 1-1 provides a high-level view of the Junos OS software architecture with its three functional processing planes. Shown above the dashed line is the control plane that runs on what is known as the Routing Engine (RE) of the Juniper device. Below the dashed line is the packet forwarding plane, which runs on a separate Packet Forwarding Engine (PFE) in larger Juniper platforms. The services plane, which provides specialized processing, ...

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