Dear NicoTing!
1. Click Advanced Configuration > Security Configuration tab, and choose MAC Address Filtering in the navigation tree on the left. In the pane on the right, after enabling MAC filter and selecting the filter mode, click New. On the dialog box that is displayed, configure the MAC filter rule for the PC to access the Internet

2. Click Apply.
The MAC address lists of PCs in the network are saved on the ONT. Configuring MAC filter rules enables the PCs that conform to the rules to access the Internet service or disables the PCs that do not conform to the rules to access the Internet service. A PC may have more than one IP addresses but a unique MAC address. Therefore, configuring MAC filter rules effectively controls the Internet service access rights of PCs in a LAN.
Thank you!