I was using Windows 10 and decided to install Ubuntu, my internet works extremly slow. On Windows 10 it worked perfectly fine. edit:
03:00.0 Ethernet controller [0200]: Realtek Semiconductor Co., Ltd. RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller [10ec:8168] (rev 09)
Subsystem: ASUSTeK Computer Inc. P8H77-I Motherboard [1043:8505]
Kernel driver in use: r8169
lspci -knn | grep Eth -A2
terminal command.