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The process of establishing a BGP peer relationship

Latest reply: Dec 18, 2018 09:51:38 2226 1 9 0 0

Hello, friends!

This post describes the process of establishing a BGP peer relationship. Please see further information on this topic as you read below.

BGP peer relationship


1. BGP generally starts with Idle State (in this case, all incoming connections are rejected). When a start event occurs, all BGP processes are initialized.

BGP resources

Enable the retry connection (ConnectRetry) timer, initialize the TCP connection to the neighbor, answer the TCP initialization message from the neighbor and the status changes to Connect.

2. The start event is a process in which an operator configures a BGP process, or resets an existing process or the router software resets BGP. This problem is caused by the process.

3. When an error occurs, the status of the BGP process changes to Idle.. The router may attempt to initiate another start event. After the first time to return to the idle state, the router automatically enables the retry connection timer, when the timer ends. After that, the router abandons the re-start of the BGP. retry timer. The first time is 60 seconds, and the next time is two times 120 seconds of the previous time, which is in the exponential form.


In this state, the BGP process determines the subsequent actions after the TCP connection is complete.

1. If the TCP connection is set up successfully, the BGP connection clears ConnectRetry, completes initialization, and sends an Open message to the neighbor.

To the Open state

2. If the TCP connection fails to be established, BGP continues to monitor the connection initiated by the neighbor, resets the ConnectRetry timer, and forwards the message to Active Status.

3. If the ConnectRetry times out in the connection state, the timer restarts and attempts to establish a TCP connection with the neighbor. In the Connect state, if there is any other input event, the call enters the Idle state.


In this state, the BGP process attempts to establish a TCP connection with the neighbor.

1. If the connection is successful, the BGP process clears the ConnectRetry timer, completes initialization, sends an Open message to the neighbor, and forwards the message to the Hold timer is set to 4mins when the Open message is sent.

2. If the ConnectRelay timer times out in the active state, it returns to the ConnectState and resets the ConnectRelay timer.

Initiates a TCP connection to the peer and continues to listen to the connection from the peer.

3. If the neighbor attempts to establish a TCP session with an unknown IP address and the ConnectRelay timer is reset, the connection is rejected and remains in the Indicates the active state.

4. Any event (except the start event) returns to the idle state.


In this state, the Open message has been sent, and BGP waits for the Open message from the neighbor.

1. If an Open message is received and an error is detected, the sends a Notification message to the neighbor and enters the Idle state.

2. If the received Open message is correct, the sends a Keepalive message to the neighbor and clears the Keepalive timer.

Negotiate a short holdtime. If the is 0, the Hold timer and the Keepalive timer are not started. Select IBGP or EBGP according to the AS number; at the same time, the status is changed to OpenConfirm.

3. If a TCP disconnection message is received, the local end disconnects the BGP connection, resets the ConnectRetry timer, and enters the Active state.


In this state, BGP waits for a Keepalive message or Notification message.

1. If a Keepalive message is received, the message is transferred to the Establish state.

2. If a Notification message is received, the state changes to Idle and the TCP connection is disconnected.

3. If the Hold timer times out and an error is detected or the stop event occurs, BGP sends a Notification message to the neighbor and disconnects the neighbor. The connection enters the Idle state.


In this state, the connection between BGP peers has been established and the Update Keepalive and Notification messages can be exchanged.

The system automatically switches to the Idle state and disconnects the connection.

  • x
  • convention:

Created Dec 18, 2018 09:51:38

If the TCP connections of two BGP neighbors are normal, but the neighbors are not always established, how should you troubleshoot them?
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  • x
  • convention:


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