Cisco do free networking courses which teach the fundamentals. The one I did was more theoretical than practical but it really helped me think of what Im really trying to achieve and learning the terminology was really helpful, especially later when trying to troubleshoot and finding help online that was a struggle before the course.
There are assessments as you progress and a certificate at the end.
They also have virtual software you can play around with for different potential configurations. Thats much cheaper than buying lots of hardware!