rm245x:

Belkin F5D8235-4 v1
lede-17.01.4-ramips-rt288x-f5d8235-v1-squashfs-sysupgrade.bin
when ports 1 and 2 are used gigabit ports auto negotiate for 100Mbit including WAN port and all seem work fine
when the same or additional cables are plugged to ports 3 and 4 gigabit ports auto negotiate for 1Gbit (while the other stay @100Mbit) and there is huge packet loss (around 50% - probably due failed autonegotiation)
ethtool package does not recognize interfaces (e.g. eth0/1) so speed/duplex cannot be set/checked.

with same cabling all ports work fine @1GBit including provider WAN connection with factory firmware.