You can check the status of an interface by issuing the ifconfig interface command. For general information on ifconfig status reporting, refer to How to Get Information About a Specific Interface.
For example, you can use the ifconfig command to obtain the status of a standby interface. When the standby interface is not hosting any data address, the interface has the INACTIVE flag for its status. You can observe this flag in the status lines for the interface in the ifconfig output.