Routing Process Architecture

The routing process is handled by the following two components (see Figure 1):

• The Routing Engine
• The Packet Forwarding Engine

Because this architecture dedicates separate control operations such as routing updates and system management from packet forwarding, the router can deliver superior performance and highly reliable Internet operation.

Figure 1: Product Architecture

Packet Forwarding Engine

The Packet Forwarding Engine uses application-specific integrated circuits (ASICs) to perform Layer 2 and Layer 3 packet switching, route lookups, and packet forwarding. The Packet Forwarding Engine forwards packets between input and output interfaces. The M-series routers (except the M7i, M40, and M320 routers) have redundant Packet Forwarding Engines. The J-series Services Routers have a software-based Packet Forwarding Engine. For more information about the Packet Forwarding Engine, see the hardware guide for your routing platform.

Routing Engine

The Routing Engine controls the routing updates and system management. The Routing Engine consists of routing protocol software processes running inside a protected memory environment on a general-purpose computer platform. The Routing Engine handles all the routing protocol processes and other software processes that control the routing platform’s interfaces, some of the chassis components, system management, and user access to the routing platform. These routing platform and software processes run on top of a kernel that interacts with the Packet Forwarding Engine. All M-series (except the M7i and M40) routing platforms and T-series routing platforms have redundant Routing Engines. For more information about routers with redundant Routing Engines, see the hardware guide for your routing platform.

The Routing Engine has these features:

• Routing protocol packets processing—All routing protocol packets from the network are directed to the Routing Engine, and, therefore, do not delay the Packet Forwarding Engine unnecessarily.
• Software modularity—By dividing software functions into separate processes, a failure of one process has little or no effect on other software processes.
• In-depth IP functionality—Each routing protocol is implemented with a complete set of IP features and provides full flexibility for advertising, filtering, and modifying routes. Routing policies are set according to route parameters, such as prefix, prefix lengths, and Border Gateway Protocol (BGP) attributes.
• Scalability—The JUNOS routing tables are designed to hold all the routes in current and near-future networks. Additionally, the JUNOS software can efficiently support large numbers of interfaces and virtual circuits.
• Management interfaces—System management is possible with a command-line interface (CLI), a craft interface, and Simple Network Management Protocol (SNMP).
• Storage and change management—Configuration files, system images, and microcode can be held and maintained in one primary and two secondary storage systems, permitting local or remote upgrades.
• Monitoring efficiency and flexibility—Alarms can be generated and packets can be counted without adversely affecting packet forwarding performance.

The Routing Engine constructs and maintains one or more routing tables. From the routing tables, the Routing Engine derives a table of active routes, called the forwarding table, which is then copied into the Packet Forwarding Engine. The forwarding table in the Packet Forwarding Engine can be updated without interrupting the routing platform’s forwarding.

In a JUNOS-FIPS environment, hardware configurations with two Routing Engines must use IPSec and a private routing instance for all communications between the Routing Engines. IPSec communication between the Routing Engines and Adaptive Services (AS) II FIPS PICs is also required.

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