When a non-recoverable error related to a particular session occurs a Notification message is sent to the peer and the session is terminated (or restarted if GR is enabled for this scenario). For more details, see BGP graceful restart. The Notification message provides the following information:
Error code
Indicates the type of error: message header error, Open message error, Update message error, Hold timer expired, Finite State Machine error, or Cease.
Error subcode
Provides more specific information about the error. The meaning of the subcode is specific to the error code.