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    Routing Engine

    The Routing Engine consists of the Junos OS running on an Intel-based Peripheral Component Interconnect (PCI) platform. The Junos OS kernel supports the Junos OS system processes which handle system management processes, routing protocols, and control functions (see Figure 1).

    The Routing Engine handles all the routing protocol processes, as well as other software processes that control the router interfaces, the chassis components, system management, and user access to the router. These routing and software processes run on top of a kernel that interacts with the Packet Forwarding Engine.

    The Routing Engine has a dedicated 100-Mbps internal connection to the Packet Forwarding Engine.

    Figure 1: Routing Engine Architecture

    Routing Engine Architecture

    Routing Engine Functions

    The Routing Engine handles all the routing protocol processes, as well as other software processes that control the router interfaces, system management, and user access to the router. These routing and software processes run on top of a kernel that interacts with the T-series Internet Processor in the Packet Forwarding Engine.

    The Routing Engine provides the following functions:

    • Routing protocol packet processing—All routing protocol packets from the network are directed to the Routing Engine, and hence do not delay the Packet Forwarding Engine unnecessarily.
    • Software modularity—By dividing the different software functions into separate processes, the failure of one process is isolated from others and has little or no effect on them.
    • In-depth Internet functionality—Each routing protocol is implemented with a complete set of Internet 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 BGP attributes).
    • Scalability—The Junos OS routing tables are designed to hold all the routes in current and imminent networks. Additionally, the Junos OS efficiently supports large numbers of interfaces and virtual circuits.
    • Management interface—Different levels of system management practices are provided, including a command-line interface (CLI) and SNMP.
    • Storage and change management—Configuration files, system images, and microcode can be held and maintained in primary and secondary storage systems, permitting local or remote upgrades.
    • Efficiency and flexibility monitoring—The router permits alarm handling and packet counting. For example, the router allows information to be gathered on every port, without adversely affecting packet forwarding performance.

    The Routing Engine constructs and maintains one or more routing tables (see Figure 2). From the routing tables, the Routing Engine derives a table of active routes, called the forwarding table, which is copied into the Packet Forwarding Engines. The design of the T-series Internet Processor allows the forwarding table in the Packet Forwarding Engines to be updated without interrupting the router’s forwarding.

    Figure 2: Control Packet Handling for Routing and Forwarding Table Update

    Control Packet
Handling for Routing and Forwarding Table Update

    On the M320 and T320 routers and the T640 router, the host subsystem provides the routing and system management functions. The host subsystem consists of the Routing Engine and the Control Board. For more information about the Control Boards and host subsystem, see Checklist for Monitoring the Control Board and Checklist for Monitoring the Host Subsystem .

    On the M40e and M160 routers, the host module provides the routing and system management functions. The host module consists of the Routing Engine and the Miscellaneous Control Subsystem (MCS). For more information about the host module, see Checklist for Monitoring the Host Subsystem . For more information about the MCS, see Checklist for Monitoring the MCS .

    On the M10i router, the Routing Engine works with its companion High-Availability Chassis Manager (HCM) to provide control and monitoring functions for router components. For more information about the HCM, see Checklist for Monitoring the HCM.

     

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    Published: 2012-08-20