Juniper Junos OS Architecture & Forwarding Engine Flow
Routing Engine (RE) calculates routing table (rib) and pushes active forwarding table (fib) to Packet Forwarding Engine (PFE)
Status: Step 1 -> BGP/OSPF peer advertises prefix updates to Routing Engine process (rpd).
Junos OS Console - MX/EX Series Enterprise Switch Router
user@junos-router> show route
user@junos-router>
What is Juniper Networks Junos OS?
Junos OS is the unified, high-performance operating system powering Juniper Networks routing, switching, and security platforms (MX, PTX, QFX, EX, and SRX series). It is built on a modular FreeBSD kernel featuring total architectural separation between control operations and packet forwarding hardware.
Core Junos Architecture & Separation
Routing Engine (RE - Control Plane): Runs administrative services, routing daemons (such as rpd), CLI sessions, and maintains the Routing Information Base (RIB / inet.0).
Packet Forwarding Engine (PFE - Data Plane): Built on custom ASICs/FPCs to execute high-speed packet lookup using the Forwarding Information Base (FIB) synchronized directly from the RE.
Candidate vs. Active Configuration: System changes occur in a candidate workspace and do not impact network traffic until validated and committed using the transactional commit engine.
Stateless Firewall Filters: Evaluates incoming/outgoing traffic at the interface level using ordered terms (Match conditions -> Action statements).
Key Junos CLI & Operational Concepts
Operational vs. Configuration Mode: Switch modes using configure or exit to move between system diagnostics (>) and hierarchy editing (#).
Commit Pipeline: Commands like commit check validate syntax prior to activation, while commit confirmed offers safety rollbacks during remote maintenance.
Routing Instances: Provides isolated routing tables similar to VRFs for enterprise network segmentation.