I have an older client, HAI Omni Pro II security system controller, that uses a static ip address that I can configure. I set the ip in the range set on my Deco system. I have 6 Deco X20 Mesh WiFi devices with a main device set up as a router and connected directly to a Spectrum cable modem and 5 satellite Deco devices around the building. Some of the satellites are connected to Ethernet and some are on WiFi. There are some switches in the system as it is a large building and the Ethernet network was added to over time during renovations, etc. For most everything I use (computers, phones, printer, Smart TV's, Tablets, etc.), this has all worked great.
The Omni has always been connected to the Ethernet network via a switch. When I was using Apple's Airport equipment for my network, I had no problem setting up an address reservation and port forwarding. I can ping the Omni from terminal on my Mac successfully so I know it is on the network. Even after switching to Deco, the Omni is on the network as indicated by successful ping on terminal.
For the Omni, I have been unable to get it to show up on the client list on the Deco app. I need to set an address reservation and port forwarding for it so I can connect to it from the phone app that allows me to control the various features it provides. In the Deco app, if its not on the client list, I can not do any configuring. Frustrating.
Today, I spent over an hour on an online chat with TPLink going through a number of things to try to get the client to show on the Deco App. This included moving a satellite Deco near the client and connecting it directly to the Deco's Ethernet port with the Deco connected to the network via Ethernet, and then WiFi. With the satellite Deco connected to the Ethernet switch on port 1 and the Omni connected to Ethernet port 2 on Deco, I can ping the Omni form terminal. When the Deco is using WiFi, and I connect the Omni to it, I can not ping the Omni in terminal.
TPLink put in a ticket to get an engineer to help me. That will not be for another couple of days ("within 1 business day" responses always happen on Saturday morning...).
My only thought is to go back to using the Airport Extreme as the Router (or a different router) and just use the Deco's to provide the WiFi.