► Get the COMPUTER NETWORKING audio book here ►https://amzn.to/3rxrkfi (Amazon affiliate). Just get the book by signing up for a free 30 day trial of Amazon Audible Premium Plus. A subnet mask is a number that resembles an IP address. It reveals how many bits in the IP address are used for the network by masking the network portion of the IP address. This video also does a short lesson on subnetting. Subnetting is breaking down a large network into smaller networks or subnets.