Realtek Ethernet Diagnostic Utility - is an official tool from Realtek to diagnose ethernet problems on many of their network cards.
This package provides installation files for Realtek Ethernet Diagnostic Utility revision 2.0.5.0 for Windows XP, Windows 7 ,Vista, Windows 8 and Windows 10.
Will work on
• RTL8111B/RTL8168B/RTL8111/RTL8168
• RTL8111C/RTL8111CP/RTL8111D(L)
• RTL8168C/RTL8111DP/RTL8111E
• RTL8168E/RTL8111F/RTL8411
• RTL8100E/RTL8101E/RTL8102E-GR/RTL8103E(L)
• RTL8102E(L)/RTL8101E/RTL8103T
• RTL8401/RTL8401P/RTL8105E
• RTL8402
• and possibly others.
Download: 
Realtek.Ethernet.Diagnostic.Utility.2.0.8.0.zip - 6.4 MB