I have been wrestling with this problem for several weeks now and obviously need help (your help?). I have a single ASUS3100 router in pretty much the default configuration. Nothing fancy. I have 3 Windows PCs and a couple of Raspberry Pi Pico-W microcontrollers all connected to the router wirelessly. All these devices are able to communicate outwardly to the internet. My problem is that most of the time, several of these devices don't see each other within the LAN. The router shows all devices with excellent signal strength. If I try to ping one PC from another, I am only sometimes successful. Usually: "Destination not found". I've tried ping -t <ip> and I get that same response for at least several minutes. When I use Thonny on a PC and execute micro-python code on a pico (to set up a server or client), I can see that the devices are successful in connecting to the router, but they can't communicate with each other. Ignoring the micro-controllers for now, why can't 1 PC see another PC ? Sometimes they see each other via ping and many times they don't. If I issue "arp -a" from a command window on a PC, the PCs don't all appear many times. Yet, ALL devices are showing up in the client list when I look at it after logging into the router itself So the router knows the devices are all there ! I've toggled AP isolation and UPnP and neither testings have shown improvement. Note that maybe 10% of the time, I can successfully ping 1 PC from another. Learning about arp ( https://www.networkacademy.io/ccna/ethernet/what-is-arp ), it seems that these PCs should be pingable from each other. What am I missing? My goal is to understand the behavior I am seeing, and then to get the micro-controllers to then talk to each other on the LAN.