Very new to network engineering. I just watched a really good series of videos on YouTube explaining IP addresses, subnet masks and the class system for IPv4.
There was one bit which got me confused however.
In lesson 2 (https://www.youtube.com/watch?v=XQ3T14SIlV4), where he goes through subnet masking, he gives an example where he uses an IP address 192.168.40.55 with subnet mask 255.255.248.0. This is at around 4:51.
However, in the subsequent lesson 3 (https://youtu.be/4xlzlgYGqW8), where he teaches default subnet masks, he says class C IP addresses must use subnet masks of at least 255.255.255.0.
Does this mean the example used in lesson 2 was false? Or is it possible to use subnet masks smaller than the default values for a given class?
Either way he got the point across very well, just want to make sure I understand everything.