If BGP peer is in idle state then it could be due to PHYSICAL connectivity failure or neighbor is not defined with properly with respective AS. In CONNECT state, BGP tries to establish TCP session over port number 179 if it fails to establish TCP CONNECTION then it goes to Active state where it retries to establish TCP connection. By using debug ip bgp and debug ip tcp transactions commands, we can find out the EXACT cause of TCP connection failure. Lack of “update-source” or “ebgp-multihop” command can ALSO be a reason for neighbor active state;

If BGP peer is in idle state then it could be due to physical connectivity failure or neighbor is not defined with properly with respective AS. In connect state, BGP tries to establish TCP session over port number 179 if it fails to establish TCP connection then it goes to Active state where it retries to establish TCP connection. By using debug ip bgp and debug ip tcp transactions commands, we can find out the exact cause of TCP connection failure. Lack of “update-source” or “ebgp-multihop” command can also be a reason for neighbor active state;