Why do i need iCOM A2 (not ENET cable) for BMW ZGM reflash?

This is a discussion about tools for BMW ZGM reflash with E-sys. BMW ICOM A2 emulator, or ENET cable? Users answer here:

SanDiegoF12: Why is an iCOM A2 required instead of just using the OBDII to Ethernet cable?

erdengurcan: ICOM A2 more stable than enet cable. For example: When you update ZGW via ENET, sometimes car stays on transport mode. But via ICOM it always come back to normal mode.

2real4u: A more technical reason is lack of DHCP server when connecting with ENET interface. This does not affect connection over DCAN, which is supported by ICOM, but cannot be accomplished with ENET cable.

Software:

Working BMW E-sys v3.22.5 and psdzdata v49.4:

http://www.eobdtool.co.uk/wholesale/bmw-enet-ethernet-to-obd-interface-cable-e-sys-icom-coding-f-series.html