BGP Session Lifecycle

The finite state machine governing every BGP peering session. Understand why 'Active' means the session is failing, how hold timers create silent blackholes, and what happens when a BGP peer goes down.

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What you'll explore

  1. 01

    FSM States

    The six states of a BGP session. Each has specific events that cause transitions.

  2. 02

    OPEN Message Exchange

    AS number, hold time, BGP identifier, optional capabilities.

  3. 03

    KEEPALIVE & Hold Timer

    The heartbeat mechanism that detects peer failure — and creates blackholes.

  4. 04

    UPDATE Message

    How prefixes are advertised and withdrawn.

  5. 05

    Session Failure & Recovery

    What happens when a peer goes down.

Validated against FRRouting frr-10.6.1 — bgpd/bgp_fsm.c and friends. Every simulated behavior cites a real source function.

The simulator is free. Unlock the full kata library, progress tracking, and weak-area analysis with zerohop Pro.

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