TP-Link 5-Port Gigabit Ethernet Network Switch

I've had two of these switches working flawless for nearly five years. Recently, I had to trip the circuit breaker resulting in reboot of both switches and several computers attached to the network. At first none of the computers were able to connect to the router or get an IP address through DHCP. If you read the little "Product Information" troubleshooting guide provided on this Amazon site, it is obviously a bunch of screen shots that walk through this very problem. They go through a series of steps involving setting up static IP addresses that will result in fixing the problem, even though it is entirely couched as gathering information rather than fixing it. ***This should not be a fix*** Why is that? Network switches don't work on the IP address level, they work on MAC addresses, which are unique to each device. So playing games with the IP addresses should not solve the issue. But this switch seems to have some smart features, particularly around IGMP that appear to block some traffic based on IP address. If you look at the details of your computers ethernet device, you will see zero received packets, and the transmitted packets slowly ticking up. This is a lockup condition. The condition works like this: 1) A computer boots up and looks for an IP address from a DHCP server. For some reason it cannot reach the server (maybe the router is down) and so it assigns itself an IP address within an autogenerated IP subdomain. 2) When the router comes up, it sends out a broadcast looking for everything that can see it within a certain IP subdomain. 3) The IP subdomains of the computer and the router are mutually exclusive. When they broadcast to do network discovery, they use multicast packets local to their subdomain. The switch does not allow these multi-cast packets to cross subdomains, so the computer and the router will never find each other. All the discovery is filtered out. If you reboot the computer. It will default to the last autogenerated IP address and the switch will filter discovery. If you power cycle the switch, it will quickly relearn the autogenerated IP address and apply the filter. If you reboot the switch, same problem--separate subdomains. The condition is locked in until you manually join the two subdomains together via static IP address allocation. The troubleshooting fix is a way to manually break this loop by putting the computer in the same subdomain as the router. This is never explained in the solution, and it makes it sound like you are just doing some debugging experiments to make sure your switch isn't broken. The the link magically starts working and you breath a sigh of relief and move on with your life. My first job was designing ASICs for network switches, so I have some familiarity with the low level workings of a switch. A dumb switch will never have this problem. It doesn't look at IP addresses, subdomains, or anything. If a packet doesn't have a specific MAC address as a destination, it will propogate the packet to all ports. My guess is the IGMP snooping feature is causing this lockup condition to occur, since it says it limits the effect of multicast packets on the network. This is not a problem any home user has to deal with. If I was going to fix this from TP-Link's side, I would probably default to dumb switch operation for first 5 minutes of operation. That allows all devices to do network discovery before the IGMP snooping/multicast filtering kicks in. With that solution, you would just have to power cycle the switch and everything would magically fix itself. As it stands, you need to do some pretty complicated network surgery to fix it. No normal user should have to mess with static IP addresses. In fact, you can cause more problems if you assign an address that is already taken. And in my case, this was not an option. I had my work laptop with the network settings locked down. I spent about 8 hours total debugging, discussing, and theorizing on the problem. I spent nearly as long googling for answers--the information is just not out there.