BGP Stuck in ACTIVE & IDLE
BGP Neighbor States – IDLE – CONNECT – ACTIVE
From this explanation we might understand that a BGP process remains in ACTIVE state is due to TRANSPORT ERROR means the BGP process is unable to initiate a TCP Connection to the Neighbor. Refer the below flow chart where it explains the FSM transitions of three states IDLE, CONNECT and ACTIVE. In real-time BGP never remain in an particular state other than ESTABLISHED. Actually it flaps between IDLE, CONNECT and ACTIVE.
BGP Stuck in IDLE
Input Events 1 & 13 causes the IDLE state remain in IDLE state. IE1 is BGP START event and IE13 is BGP Notification Received. Also IE 2, 4, 6, 8, 9, 13 causes other BGP states to transit back to IDLE. So the possible reason for a BGP router remain in IDLE is mentioned below.
- Neighbor Route is not present in Routing Table.
- TCP 179 is not open.
- BGP Configuration Error like wrong AS in running-config causes the BGP to set a NOTIFICATION which lead to the FSM fail back to IDLE.
BGP Stuck in ACTIVE
Input Event 5 cause the ACTIVE state to remain in ACTIVE state. Which is BGP TCP Open Failed. In a situation where neighbor tries to open a TCP connection using invalid or wrong IP address causes BGP to stuck in ACTIVE. The possible reasons are mentioned below.
- Peer address configured incorrectly on either router.
- AS number configured incorrectly on either router.
- Update Source configured incorrectly.
- Both the peers are in passive Transport mode or both are in active Transport mode.
- Link flapping, reverse route not present, network congestion.
LAB EXAMPLE – BGP Stuck in ACTIVE and IDLE
For the simulation of the topology we have misconfigured one router.