What are BGP neighbor states?
In the Border Gateway Protocol (BGP), a neighbor state refers to the current status of the relationship between two BGP routers that have established a connection with each other. BGP uses a finite state machine to manage the connection between two neighbors, and there are several different neighbor states that a connection can be in at any given time.
The six main BGP neighbor states are:
- Idle: This is the initial state of a BGP connection, and it means that the router is waiting for a BGP connection to be established.
- Connect: This state indicates that the router is trying to establish a TCP connection with its neighbor.
- Active: In this state, the router is trying to establish a BGP connection with its neighbor, but has not yet received a response from the neighbor.
- OpenSent: This state indicates that the router has sent an Open message to its neighbor, but has not yet received a response.
- OpenConfirm: This state indicates that the router has received an Open message from its neighbor, and is waiting for the neighbor to confirm the connection.
- Established: This is the final state of a BGP connection, and it means that the connection between the two routers is fully established and operational.
In addition to these main states, BGP also has several other states that can be used to indicate specific conditions or errors. For example, there are states for handling hold times, retrying connections, and handling errors or malfunctions.