The value of tBgpInstanceEnforceFirstAS specifies whether the receipt of BGP routes from an eBGP neighbor should be classified as an error when it has an AS-Path with the most recent AS not matching the configured peer-as of the neighbor. If the value is set to 'true', the most recent AS number in the AS-Path will be checked for every received route from the peer or set of peers to match the peer's configured peer-as. If it does not match, then the session will be reset if the update-fault-tolerance under error-handling is not configured. Else, the session will not be reset, but all the prefixes in the received update will be treated as withdrawn and logged. It is applicable to all the address families and only to true eBGP sessions.