Connect a client to LAN but not to WAN - how?

Routers
1

I have a Beryl MT1300. How can I configure it so that one client (ethernet connection) can communicate with other local clients via LAN, but not with the internet? I still want the other clients to access the internet, just not this one.

3

You can set up firewall rules via SSH to deny data sent by the device to the external network and retain communications within the LAN.
iptables -I FORWARD -s 192.168.8.199 ! -d 192.168.8.0/24 -j REJECT
Test information:
Special client: 192.168.8.199
Local LAN segment: 192.168.8.0