About a week ago I lost the connection to my Canon printer from both my 21.3 machines. My Windows boxes were still connected to the printer. After many hours trying to work out why the connection had gone and why neither of my Mint machines could see my printer never mind connect to it I finally stumbled on the reason. Connecting to my printers settings page using it's IP address and going though all the settings I found that the Bonjour service had been disabled. As Bonjour is needed in (as far as I understand) Linux for discovery that immediately explained why I had both lost the connection in the first place and could not then discover my printer no matter how many times I tried.
Enabling the Bonjour service again restored sanity. My printer was instantly discovered and enabled on both machines. But that left the question of why Bonjour was disabled in the first place?
I have two Synology NAS home servers. One is a backup and one is my main server. As my main NAS is available on the internet I regularly do security audits on it, specifically looking for services running that could conceivably be used by an outside intruder.
In Synology's Control Panel - File Services - Advanced there is an option to enable Bonjour service discovery to locate DiskStation. This is for locating DiskStation using MacOS but underneath this is an option to Enable Bonjour Printer Broadcast.
I can dimly remember turning both of these options off about a week ago. I had turned them on again immediately as I remembered I have an American friend who has an M1 Mac and who stays with me from time to time. I also quite a few years ago had another Canon printer connected to my servers USB port and which then became a shared network printer. Hence the need for Enable Bonjour Printer Broadcast option.
So what has this to do with Mint and non discovery of printers? Turning these options off does for some reason unknown to me turn off Bonjour service in my Canon printer! I can only assume it turns off Bonjour across the whole network! But turning them on again does nothing, the Bonjour service has to be turned on manually in my printer settings page.
So in conclusion, do not turn off Bonjour in your Synology NAS as you may then lose all connections to your printer!
A very long winded post but hopefully this may help someone else along the way.
