Each IBox "port" has its own set of interlock logic and state. So the ECOM100 instruction is for the ethernet port on the ECOM100 module in (say) slot 2. The NETCFG instruction is (say) for the local serial port (KF2?), but you could add a DCM module and have ANOTHER NETCFG instruction for the serial port in the DCM module in (say) slot 3.
You can't mix RX/WX/NETRX/NETWX and MRX/MWX on the same serial PORT. As a Master, your slaves must ALL be Modbus or ALL be DirectNet on THAT port's network. However, the local serial port could be Modbus and you would not use NETCFG/NETRX/NETWX/RX/WX, but just use MRX/MWX with your own interlocking. However, the DCM in slot 3 WOULD use NETCFG/NETRX/NETWX if it was a DirectNet network.
You technically CAN mix/match RX/WX with NETRX/NETWX and ECRX/ECWX on the same port, but I recommend that (if possible), you stick with ALL IBoxes on that network. If you DO need to mix them, make sure your RX/WX rungs are BELOW ALL NETRX/NETWX ECRX/ECWX IBoxes. NETRX/NETWX/ECRX/ECWX IBoxes know how to play fair with RX/WX, but RX/WX do not know how to play fair with those IBoxes, so IBoxes must appear BEFORE the native RX/WX instructions.