This read-write attribute, when enabled, restricts the ComPort to forwarding only ARP broadcast packets upstream, with all other traffic blocked; default is disable. It's a way to put a STU into a highly restricted mode - useful during initial provisioning or troubleshooting when you want basic address-resolution traffic to pass but nothing else. For example, during initial install before full service is activated, provisioning might temporarily enable stuEtherForwArpOnly so the STU only relays ARP traffic until the account is fully turned up.