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Operating System Infrastructure and Processes

Junos OS Evolved includes the processes that run the device, including IP routing, Ethernet switching, managing interfaces, and a variety of other functions.

Junos OS Evolved runs on the Routing Engine. The Routing Engine kernel coordinates communication among the software processes and provides a link to the Packet Forwarding Engine.

Using the CLI, you configure device features and set the properties of network interfaces. After activating a software configuration, use the CLI user interface to monitor, manage operations, and diagnose protocol and network-connectivity problems.

Routing Engine and Packet Forwarding Engine

A Juniper Networks router or switch has two primary software processing components:

  • Packet Forwarding Engine—Processes packets; applies filters, routing policies, and other features; and forwards packets to the next hop along the route to their final destination.

  • Routing Engine—Provides three main functions:

    • Maintains the routing tables used by the network device and controls the routing protocols that run on the device.

    • Packet forwarding, which provides route lookup, filtering, and switching on incoming data packets, and then directs outbound packets to the appropriate interface for transmission to the network.

    • Provides control and monitoring functions for the device.

Junos OS Evolved Processes

The Junos OS Evolved software running on the device consists of multiple processes that are responsible for individual functions.

The separation of functions provides operational stability, because each process accesses its own protected memory space.

The following table describes the primary software processes.

Table 1: Junos OS Evolved Processes




Chassis processes

hwdre (Routing Engines) and hwdfpc (FPC nodes)

Detects hardware on the system that is used to configure network interfaces.

Monitors the physical status of hardware components and field-replaceable units (FRUs), detecting when environment sensors such as temperature sensors are triggered.

Relays signals and interrupts—for example, when devices are taken offline, so that the system can close sessions and shut down gracefully.

Distributor process


Spawns on each node of the system. Holds the distributed data store (DDS) and coordinates with individual applications for delivery of their state. The distributor process synchronizes state across the system.

DNS server process


Resolves hostnames into addresses.

Dynamic Host Configuration Protocol (DHCP) process


Enables a DHCP server to allocate network IP addresses and deliver configuration settings to client hosts without user intervention.

Forwarding process


Defines how routing protocols operate on the partition. The overall performance of the partition is largely determined by the effectiveness of the forwarding process.

Interface process


Manages all interfaces on the device. Ifmand creates all operational states related to interfaces as well as the necessary interface-specific routes and next hops.

Management process


Provides communication between the other processes and an interface to the configuration database.

Populates the configuration database with configuration information and retrieves the information when queried by other processes to ensure that the system operates as configured.

Displays operation and configuration state of the device in text, XML, or JSON format when interfaced by the user.

Routing protocol process


Defines how routing protocols such as RIP, OSPF, and BGP operate on the device, including selecting routes and maintaining forwarding tables.

Simple Network Management Protocol (SNMP) process


Enables the monitoring of network devices from a central location and provides the switch’s SNMP master agent.