I covered BGP Peer/Neighbor states. This will allow you to successfully analyze and troubleshoot BGP peer relationships and states. BGP goes through the following states when establishing a BGP session with neighbor.
Idle State: Idle state is the initial state of a BGP connection. Router is searching Routing table to see whether a Route exits to reach the neighbor.
Connect State: Router found a Route to the neighbor and it will complete the three-way TCP handshake. The BGP speaker is waiting for a start event, generally either the establishment of a TCP connection or the re-establishment of a previous connection. Once the connection is established, BGP moves to the next state.
Open sent State: Open message sent to peer with the parameters for the BGP session.
Open confirm State: Router received agreement on the parameters for establishing session, the state moves to Established and the neighbor relationship is complete.
Active State: Router goes in to active state if on response from Peer to open message.
Established State: Peering is established and Routing update packets are actually exchanged.
Filed Under: BGP
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