JUNOS Processes Supported Networking Standards The JUNOS Internet software provides IP routing protocol software ”as well as software for interface, network, and chassis management ” specifically designed for the large production networks typically supported by Internet service providers (ISPs). The JUNOS Internet software runs on all Juniper Networks M-series and T-series routers and routing nodes. Architecturally, the router is composed of two components as shown in Figure 2.1: -
Packet Forwarding Engine ”Forwards packets through the router. The Packet Forwarding Engine is a high-performance switch that is capable of forwarding 40 million packets per second for any packet size. The Packet Forwarding Engine forwards packets between input and output interfaces. The function of the Packet Forwarding Engine can be understood by following the flow of a packet through the router ”first into a PIC, then through the switching fabric, and finally out another PIC for transmission on a network link. When a packet arrives on an input interface, a media-specific PIC performs all media-specific functions such as framing and checksum verification. -
Routing Engine ”Performs 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 has a direct 100-Mbps connection to the Packet Forwarding Engine. Figure 2.1. Juniper Networks Router Architecture  | See "Router Architecture" on page 28. | Because this architecture separates control operations such as routing updates and system management from packet forwarding, the router can deliver superior performance and highly reliable Internet operation. The Routing Engine handles all the routing protocol processes and other software processes that control the router's interfaces, a few of 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. Following are the features of the Routing Engine: -
Process routing protocol packets ”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 the other software processes. -
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 length, and BGP attributes. -
Scalability ”The JUNOS routing tables are designed to hold all the routes in the network. 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, SNMP, and JUNOScript. -
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 copied into the Packet Forwarding Engine. The forwarding table in the Packet Forwarding Engine can be updated without interrupting the router's forwarding. |
