Though this is straight from the administration guide:
Mirror Source Use this to enable or disable source port mirroring for each port on
the router. To enable source port mirroring on a port, check the box next to that
port. To disable source port mirroring on a port, leave the box unchecked. The
default is disabled.
Mirror Port Select the mirror destination port from the drop-down menu.
However if you are not given the options by default it should be set at both.
I will try to confirm this and get back to you.
Thank you,
Mike
