shutting down the dataguard physical standby

when shutting down the physical standby using sqlplus it appears that the primary is also being shutdown.  should i be shutting down the standby using the dataguard broker ?  We don't normallly shutdown the standby, but under some circumstances  like a server reboot we would. I've noticed that the last two times we shutdown the standby, the primary also shutdown, and after atteending a dataguard broker webex where they suggested everthing be done thru the broker, i got to wondering if the startup and shutdown of the standby should be done thru the broker ?