I want to connect 1000Base-T Ethernet to 100Base-TX Ethernet. 1000Base-T MDI lines have 8 signals whereas 100Base-TX has 4 signals. Does this create any problem if I connect both of them or auto-negotiation works such a way that only 4 signals will be used from 1000Base-T? Thanks
All consumer hardware you encounter that can do 1000Base-T (Gigabit Ethernet) can also do Fast Ethernet (100Base-TX) and will downgrade as necessary. Auto-Negotiation just works.
Doesn't apply to all hardware, though. I know of a class of sampling devices whose ethernet frames need Gigabit Ethernet, so they simply don't work with 100Base.