The LAN cable from downstairs was not connected to the second router, it was connected to the laptop directly: excluding the second router from the network.
Maybe the 2nd router had a rogue DHCP enabled, and the technician used ipconfig to wipe that lease from the laptop.
So you are assuming that the tech checked his setup, said his config was wrong and only went as far as making sure the internet worked on his laptop? Hahaha. No, the tech did his job. He checked to make sure the AP was functioning properly and then made sure the second router was set as a bridge. The OP didn't give us any information on his setup other than that he ran a wire from the AP to the second router. I'll just have to assume that he himself set the second router to bridged mode and attached it to the AP.
I am not assuming anything, i read the lttle info given To me this is the same as: "a technician fixed my car, how did he fix it". Yes, less to none info given
The technician connected to both routers. Green: to router of living room Blue: to router of bedroom I love puzzles...and I like rational thinking.. OP said he purely used ipconfig commands to resolve the issue. He connected to the router of the living room first while the connection from router in the living room to router in bedroom was not made! Then he connected the router from living room with the router of bedroom first and then he connected the laptop to the router of the bedroom. It seems like a network misconfiguration which is resolved by re-announcement of DNS. I assume the router of the living room runs the (only) DHCP. Also the way / order of to unplug / re-plug makes the router to reassign IP / re-announce DNS... It is of course difficult to figure what was really wrong, but ipcionfig commands usually cannot do much.... I totally agree. +1 Maybe ipconfig /flushdns as well