Asus TM-AC1900 User Manual page 60

MAC Address: MAC (Media Access Control) address is a
unique identifier for your networking device. Some ISPs
monitor the MAC address of networking devices that connect
to their service and reject any unrecognized device that
attempt to connect. To avoid connection issues due to an
unregistered MAC address, you can:
with your ISP service.
to match the MAC address of the previous networking device
recognized by the ISP.
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