Many of you have complained about losing the LAN connection to their Surface after updates and not been given a reasonable of what to do about it, or one that works. This is where the digital and analog worlds collide and it goes something like this: You have a signal coming into your computer but, before it gets there, it goes through a modem, then a router, powered or passive, wired or wireless. Every time you split a signal, it gets weaker, in strength and in the fidelity of the info it carries. Digitizing info made great advances in keeping the fidelity (i.e. the minimum of amount of required info to accomplish the end result) in tact but, that does for the strength and unless the strength is at a certain minimum, it won't be detected. When you are dealing with low voltages (the overall voltage of the signal out of your router) this gets critical. Any oxidation on the pins of your cat5, 6, etc. connection will make the signal seem non-existent, (even though the digital signal is there and readable, just not loud enough to be heard).
The solution is good cables, the right selection of active and passive equipment, and coping with problems that age engineers well before their time. Not saying I know it all but, I've got a Bachelors in information systems and some 50 years experience starting with Presidential Communications. Take my ideas for what they're worth.