I was asked at the end of today’s lecture whether there was additional information to help understand subnets. Here are some pointers:
1) Take a look at the website for Behrouz Forouzan’s “TCP/IP Protocol Suite” (the course text). There are some powerpoint slides for chapter 5 (the chapter on subnetting) that go into considerable detail about subnetting and CIDR.
2) Wikipedia has an entry that (at the moment at least) is substantially complete.
3) Tech Republic has an IP subnetting made easy article, which claims to provide a clear and graphical method of understanding subnets. I am not sure if I agree that this site is particularly clear, but on the basis that different people learn differently, I offer it up. Please comment to let me know if it helps or not.