Hey there
I've got a DSL-2750U U1 (white casing) ADSL router. A few days ago I had to hard-reset and reconfigure it. I did it an after that the local services like ftp, rdp, samba, dnla (between my smart TV and android devices) etc have stopped working between the devices connected through the LAN cable but they work properly when all the clients and servers are connected wirelessly
I didn't touch any Advanced configuration in the router, also tried solving it by completely turning off the firewall feature in the menu, no chance