1 – Idle
2 – Connect
3 – OpenSent
4 – OpenConfirm
5 – Established
6 – Active
TheBGP finite state machinedefines how a BGP speaker transitions through various states when establishing and maintaining a BGP session. Below is the role of each state:
Idle (1)– BGP is waiting to start a connection. Initial state of the BGP process.
Connect (2)– BGP initiates a TCP connection to the peer.
OpenSent (3)– TCP connection is established; BGP sends an OPEN message and waits for one from the peer.
OpenConfirm (4)– BGP has received a valid OPEN message and is now expecting a KEEPALIVE.
Established (5)– BGP session is fully established; UPDATE messages can now be exchanged.
Active (6)– If the TCP connection fails in Connect state, BGP transitions to Active and will retry connection.
Reference from Huawei HCIP-Datacom-Core Technology Study Guide:
“BGP goes through the following states in order: Idle → Connect → Active → OpenSent → OpenConfirm → Established. The transition depends on the success or failure of TCP connection setup and BGP message exchanges.”
(Chapter: BGP Principles – Section: BGP State Machine)
