Are you truly physically connecting/disconnecting the network cable, or are you doing something related/similar instead, such as disabling the network adapter or disconnecting it in the virtual machine?

Can you first clarify the symptoms please?

Are you saying that when you call DiscoverServers *without parameters* (resulting in a search on the local machine), it will discover the local OPC UA server properly when the network cable is connected, but not when it is disconnected? And what happens when the network cable is disconnected? Do you get an error (details please) - or no error, but an empty collection as a method result?

Thank you

Have a look at the FindApplications method (an extension method to IEasyUAClient, in IEasyUAClientExtension class). You can pass in a list with e.g. just one discovery URL.

But there is something wrong if, as you wrote, "DiscoverServers [...] works only as long as the network is connected.". For a client and server on the same machine, that's not normal.

This should work and is one of the common scenarios. Make sure that:

1) OPC UA Local Discovery Server (LDS) is installed and running
2) The OPC UA server is running and successfully registering with the LDS.

Some servers (but they are typically embedded servers where LDS is not present and makes no sense - this is obviously not your case as you are on a PC) do not register themselves with a LDS.

In addition, every OPC UA server acts is its own "mini-LDS", being able to provide info about its own endpoints. This works even without 1) and 2) above, and this functionality can also be accessed by QuickOPC (in a more complicated way), but I would not call it "server discovery", because you actually need to know at least the protocol and server port upfront. It is meant for discovery of different endpoints of an already known server.

Regards