BGP FSM Idle State

BGP employs a BGP - Finite State Machine (FSM) to establish and maintain peerings between BGP routers, and to exchange routing information.

During the IDLE state of the BGP FSM, several critical system-level resources are initialized to prepare for neighbor connection establishment:

Memory Allocation

  • Allocates memory for session-specific data
  • Stores BGP messages, routing tables, and neighbor state information

Data Structures Setup

  • Initializes internal data structures for BGP session management
  • Creates neighbor entries in session tracking tables
  • Prepares route tracking tables

Timer Configuration

Event Handling Setup

  • Prepares mechanisms for handling BGP events and transitions
  • Ensures FSM readiness for state changes
  • Sets up handling for TCP connection events and session resets

TCP Socket Setup

  • Opens TCP socket
  • Configures listening for incoming neighbor connections

Log Initialization

  • Starts/resets logging mechanisms
  • Prepares for session establishment tracking
  • Sets up debug information logging

These system-level initializations are internally managed by BGP and not user-configurable. They ensure BGP's readiness for subsequent FSM states, particularly the transition to Connect state upon successful TCP connection.

https://networklessons.com/bgp/bgp-neighbor-adjacency-states