If you have an OpenWRT router, sometimes you need to block particular devices from accessing internet yet still can connect to its Wi-fi network. We can do that easily from the LUCI web-UI control panel.
Head for menu Network > Firewall.
There you can make a new firewall rule. Give it a name in New forward rule section. Then click Add and edit.
Then you have to choose the device’s MAC address to block.
Then choose option Reject in the Action dropdown list.
Then click Save and apply. Make sure you have the new rule is listed in the rules list.