Asus GigaX2124X/C - Manual (Page 40)

GigaX Series L2 Managed Switch User’s Guide
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The monitor port can not belong to any link aggregation group.
The monitor port can not operate as a normal switch port. It does
not switch packets or do address learning.
4 ports are only supported for mirror egress port.
Click to make the setting send to the switch (HTTP server). Click
to refresh the settings to current value.
Figure 19. Mirroring page