I inherited an industrial setup with 20–30 controllers mounted on moving booms. The controllers do not have built-in Wi-Fi, so each one connects through a TP-Link TL-WR902AC configured in client mode. Unfortunately, every unit still has the default hostname, making it difficult to tell which device is having problems. The MAC address labels are covered by industrial adhesive, and the units are mounted inside secured boxes about 10 feet up, so accessing them physically is difficult. They also do not appear to respond to CDP or LLDP while operating in client mode. I know the IP addresses of the controllers and access points. Is there a practical way to map each boom or controller to its corresponding Wi-Fi client and MAC address without individually rebooting or removing the units?
4 Answers
If you can generate traffic from a particular controller, you should be able to identify it without rebooting anything. For example, start a ping from the controller or send traffic to a known host, then watch the wireless association or client table on the access points. The client that becomes active is the bridge connected to that controller. You can also use the controller's IP address and the ARP table to associate the controller with its MAC address, then record the mapping for each boom.
For a physical location check, a temporary access point on a portable stand can help. Walk around the facility and compare signal strength from each bridge, or use the wireless controller's signal readings to narrow down where a client is mounted. That avoids climbing to every box, though it may take some time and works best when the units are spread out enough for their signal levels to differ.
Since you already know the controller IPs, make a table containing each controller IP, its ARP-resolved MAC address, and the access point or wireless client it maps to. If you need to confirm the physical location, ping all the controllers continuously and reboot one bridge during a planned maintenance window while the booms are parked. The controller that disappears identifies that unit. It is disruptive, but it is reliable and only needs to be done once per device.
Be careful with using a small Ethernet switch to identify the devices. The LAN MAC address and the Wi-Fi MAC address belong to separate interfaces, so the address shown by the switch may not be the one used by the wireless network. ARP and DHCP tables on the router or firewall are more useful for finding the IP-to-MAC relationships. LLDP generally will not cross the wireless client connection, although it may work on the local Ethernet side if the TP-Link supports and has it enabled.
Doing this after the equipment is parked is probably the safest approach. Once the mapping is recorded, you can rename the devices and avoid repeating the process.