New MB <-> old MBP cabling problems
So to connect a new MB to an old MBP via cables is, at best, a kludge: cable 1: USB-C to USB; cable 2: USB to Ethernet; cable 3 Ethernet.
This is a direct connection, not through the intranet.
With the old MB and old MBP, a single ethernet cable direct-connects, and all "just works".
With the new MB and old MBP, and the 3 cables, it most certainly does NOT "just work".
Logically enough, the MB sees is as a USB connection; the MBP as an ethernet connection in System Preferences - Network.
The connection would sometimes appear, then disappear, and so on.
Eventually, I "solved" this by assigning a fixed IP, using free addresses in the intranet, to each end. Sometimes that made a slow connection, sometimes as fast as it should be [50 GB file in 10 min (which is why WiFi is not an option)].
Copying an iPhoto album, also ~50GB, also does not work - Finder simply quits on the transfer after a while.
However, zipping the album into a single file [still around 50GB after zipping], lets Finder copy it from MBP to MB.
The 'genius' at the local Apple store had no solution, and took a while to understand the DHCP-manual setting that I came in with.
There's got to be a better way ...
