Article ID: 4875
Maximum link distance for 1000Base-T
Gigabit link cannot be established
The maximum link distance for a full duplex 1000Base-T Gigabit Ethernet link utilizing four pairs of Category 5 UTP cabling is 100 meters.
This distance is stated in the 802.3ab Ratification press release
Unless all four pairs are utilized for 10/100/1000 port attachment, the peer ports may or may not be able to attain link; and if they attain link, they will likely not be able to reliably pass traffic. This is true of both straight-through and crossover pinouts, at any line speed.
See also: 4593