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System Architecture Flashcards

6 cards from real JNCIA practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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  1. What is the Routing Engine (RE) responsible for in Junos architecture?

    Answer: Running routing protocols, managing configuration, and maintaining the routing table

    The Routing Engine runs the Junos OS kernel, executes routing protocols (OSPF, BGP), maintains the routing and MPLS tables, and handles management plane functions.

  2. What does the Packet Forwarding Engine (PFE) do in Junos?

    Answer: Forwards transit packets at line rate using the forwarding table programmed by the Routing Engine

    The PFE is the data plane component that performs high-speed packet forwarding using Application-Specific Integrated Circuits (ASICs), using the FIB programmed by the Routing Engine.

  3. In a dual-RE Junos chassis, what is the function of the backup Routing Engine?

    Answer: Maintains a synchronized copy of the routing state and can take over as master if the primary RE fails

    The backup RE stays synchronized with the primary RE via GRES and NSR, allowing near-instantaneous RE failover without disrupting protocol adjacencies or active sessions.

  4. What Junos process is responsible for managing routing protocols?

    Answer: rpd (Routing Protocol Daemon)

    The Routing Protocol Daemon (rpd) is the primary process managing all routing protocols including OSPF, IS-IS, BGP, RIP, LDP, RSVP, and PIM in Junos OS.

  5. What is the significance of the 'inet.0' routing table in Junos?

    Answer: It is the main IPv4 unicast routing table used for unicast forwarding decisions

    inet.0 is the default IPv4 unicast routing table in Junos. All IPv4 unicast routing protocols (OSPF, BGP, static, connected) install routes here for forwarding decisions.

  6. How does Junos OS ensure software modularity and fault isolation?

    Answer: By running each major function as a separate process (daemon) that can restart independently without affecting others

    Junos OS uses a microkernel architecture where separate daemons handle routing, management, chassis, SNMP, and other functions. A daemon crash only affects that function, not the entire system.

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Sources & references

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  1. learningportal.juniper.net — Test delivery, eligibility, exam format, score release, time limit, exam information · verified Nov 2026
  2. juniper.net — Passing score, score validity, renewal · verified Oct 2026