SMC Networks Wireless Broadband Router - Manual (Page 28)

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Function of buttons:
MAC Level... The “Access Control” is based on IP addresses only. If a user
is able to change his/her IP address, then s/he will not be
controlled by this function. The “MAC level” access control
allows you to control the mapping of MAC addresses and IP
addresses. You can also control which MAC address is allowed
to connect to this device.