Realtek NIC running at 100Mb/s rather than 1000Mb/s

Solution 1:

As others have already noted you need to be connected to a gigabit switch and, of course, there will need to be other gigabit enabled computers connected to that switch to get any practical benefit.

Note that if you are using a garden variety router/modem/switch it is almost certainly going to only be 100Mbit.

The other thing to be wary of is the cables being used. Yesterday I tracked down a similar problem in my own network where one of the computers would only connect at a slow speed. It turned out to be a dodgy Ethernet cable. You will need cables marked as Cat5E or, preferably, Cat6.

Solution 2:

If you are definately sure you're using a gigabit switch, you need to ensure that all the devices on the network (including the switch) are capable of auto negotiation. Otherwise, the devices will not show and operate correct speeds, and you'll have what's known as a Duplex Mismatch.

Other useful links on the topic:

• Ethernet
• Auto Negotiation

Solution 3:

Where do you plug the ethernet cable into?
Is it a switch/router that only supports 100Mbit/s? If yes, then that's the problem.