Juniper Basic

Junos Operating System Fundamentals(Part - 1)

• Robust, Modular, and Scalable

Junos OS functionality is compartmentalized into multiple software processes.Each process handles a portion of the device’s functionality. Each process runs in its own protected memory space, ensuring that one process cannot directly interfere with another. When a single process fails, the entire system does not necessarily fail.This modularity also ensures that new features can be added with less likelihood of breaking current functionality.The Junos OS is the trusted, secure network operating system powering the high-performance network infrastructure offered by Juniper Networks. The Junos kernel is based on the FreeBSD UNIX operating system, which is an open-sourcesoftware system.

• Single Source Code Base

All platforms running the Junos OS use the same software source code base within their platform-specific images.This design ensures that core features work in a consistent manner across all platforms running the Junos OS.Because many features and services are configured and managed the same way, the setup tasks and ongoing maintenance and operation within your network are simplified.

• Separate Control and Forwarding Planes

Another aspect of Junos modularity is the separation of the control plane and the forwarding or data plane. The processes that control routing and switching protocols are cleanly separated from the processes that forward frames, packets, or both through the device running the Junos OS. This design allows you to tune each process for maximum performance and reliability. The separation of the control and forwarding planes is one of the key reasons why the Junos OS can support many different platforms from a common code base.

The graphic illustrates a basic view of the Junos architecture and highlights the control and forwarding planes. The control plane, shown above the dashed line on the graphic, runs on the Routing Engine (RE). The RE is the brain of the platform; it is responsible for performing protocol updates and system management. The RE runs various protocol and management software processes that reside inside a protected memory environment. The RE is based on an X86 or PowerPC architecture, depending on the specific platform running the Junos OS. The RE maintains the routing tables, bridging table, and primary forwarding table
and connects to the Packet Forwarding Engine (PFE) through an internal link. Although all Junos devices share this common design goal, the actual components that make up the control and forwarding planes vary between the different Junos devices.For additional details about a specific Junos device. 

The PFE, shown below the dashed line on the graphic, usually runs on separate hardware and is responsible for forwarding transit traffic through the device. In many platforms running the Junos OS, the PFE uses application-specific integrated circuits (ASICs) for increased performance. Because this architecture separates control operations—such as protocol updates and system management—from forwarding operations, platforms running the Junos OS can deliver superior performance and highly reliable deterministic operation. The PFE receives the forwarding table (FT) from the RE by means of an internal link. FT updates are a high priority for the Junos OS kernel and are performed incrementally.Because the RE provides the intelligence side of the equation, the PFE can simply perform as it is instructed—that is, it forwards
frames, packets, or both with a high degree of stability and deterministic performance. This architectural design also makes possible the incorporation of high availability features like graceful Routing Engine switchover (GRES), nonstop active routing (NSR), and unified in-service software upgrades (ISSUs).