I'm currently trying to get a new Pi3B+ into our institutes ethernet network (maybe I should have taken off during these days
The old Pi3B are connecting without any problem with the ethernet. The new Pi3B+ doesn't come out of the eth0 configuration state (using the latest Raspbian Stretch from 13.11.2018). I can see the available Wifi connections, but the one I need to use is greyed out and not accessible (probably not accessible for an unknown user, I might configure this later with my user credentials in wpa_config).
What did I try so far:
I exchanged the SD card with one of the old Pi3B (Stretch with Jessie), but then the Pi3B+ doesn't boot at all (the multicolor screen appears).
If I use the new Stretch with an old Pi3B then the network connection doesn't work either...So I guess it's a software update issue from Jessie to Stretch (?).
I copied also the complete /etc/network folder from Jessie into Stretch...no success
I try now to make a dist-upgrade with an old raspbian Jessie that works on an old Pi 3B and see, if I can get it running in the 3B+ after I succesfully tested the network connection with the 3B.
OK while written this text the dist-upgrade finished and my old Pi3B booted and the ethernet connection worked fine: "Your Raspbian system has been updated to the latest version...."
Now I try this SD card with the new Pi3B+:
OK no way...again the nice multicolor screen.
BTW in my private home network Stretch is working well with a Pi3B and Wifi and ethernet connections are working properly there (also no fix IP address). This evening I will take a Pi3B+ home and check if it's also working there...then I could exclude hardware and software issues and check next week with our system admin what could be the reason.
Have a nice start into the next year and all the best!