Broken Ethernet Port

Long time browser of the forum, first time asker. I have a weird issue that has cropped up and would like to know the best approach at resolving it. I have a custom single board computer(running linux) that does some measurements. It has a built in ethernet port that has been in use before for...

I just replaced my ethernet cable a few days ago, but now often suddenly my ethernet conection just goes away. The cable is in perfect conditions, Maybe is the modem? or I damaged the lan port from my mobo?