Junos OS Architecture Overview
This topic provides an overview of the Junos OS product and routing process architecture:
Junos OS provides IP routing software as well as software for interface, network, and
chassis management. Junos OS runs on all Juniper Networks
J Series, M Series, MX Series, and T Series routers, as well as on other Juniper Networks products.
J Series Services Routers are deployed at the remote edge of distributed networks.
M Series Multiservice Edge routers are mostly deployed in small and medium cores in peering, route reflector, data center applications, or at the IP or MPLS edge to support high-performance Layer 2 and Layer 3 services. All M Series routers have redundant power and cooling, and the M10i, M20, M40e, M120, M160, and M320 routers have fully redundant hardware, including Routing Engines, switch interface components, and packet forwarding components. The M120 router also supports Forwarding Engine Board (FEB) failover. In the event of a FEB failure, a backup FEB can quickly take over packet forwarding.
MX Series 5G Universal Routing Platforms are Ethernet-optimized edge routers that provide both switching and carrier-class Ethernet routing. The MX Series routers support Dense Port Concentrators (DPCs), Modular Port Concentrator (MPCs) and Modular Interface Cards, and FPCs and PICs. For a detailed list of supported line cards see the MX Series Interface Module Reference.
T Series Core routers (T320, T640, T1600, T4000, TX Matrix, and TX Matrix Plus routers) are deployed at the core of provider networks. These routers have fully redundant hardware, including power and cooling, Routing Engines, and Switch Interface Boards (SIBs).
A routing matrix is a multichassis architecture composed of multiple routers, for example, one TX Matrix router connected to one to four T640 routers, or one TX Matrix Plus router connected to one to four T1600 routers. From the perspective of the user interface, the routing matrix appears as a single router. On a routing matrix composed of a TX Matrix router and T640 routers, the TX Matrix router controls all of the T640 routers. On a routing matrix composed of a TX Matrix Plus router and T1600 or T4000 routers, the TX Matrix Plus router controls all the T1600 or T4000 routers.
Routing Process Architecture
The routing process is handled by the following two components (see Figure 1):
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.
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) have redundant Packet Forwarding Engines. The J Series Routers have a software-based Packet Forwarding Engine.
The Routing Engine controls the routing updates and the 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 of the routing protocol processes and other software processes that control the routers’ interfaces, some of the chassis components, system management, and user access to the router. These routers and software processes run on top of a kernel that interacts with the Packet Forwarding Engine. All M Series (except the M7i and M40) routers and T Series routers have redundant Routing Engines.
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 unnecessarily delay the Packet Forwarding Engine.
Software modularity—Software functions are in separate processes, so 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—Junos OS routing tables are designed to hold all the routes used in current and near-future networks. Additionally, Junos OS can efficiently support large numbers of interfaces and virtual circuits.
Storage and change management—Configuration files, system images, and microcode are held and maintained in one primary and two secondary storage systems, permitting local or remote upgrades.
Monitoring efficiency and flexibility—Alarms are generated and packets are 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 router’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.