So I made a non-steam server for CS: Source and forwarded the port but I could only access it through LAN, in other words it wasn't showing up in the internet section of the server browser. I connected it directly to the cable modem and it showed up in the internet section but my friend was unable to join, couldn't find it in favourites, and couldn't join through steam community (it said that the server wasn't responding). Any suggestions?
Make sure you have all the ports forwarded correctly. Go to portforward.com.
It could be because of your bandwidth or a setting that he is having difficulty joining. Minimum ping/ max ping and all that.