• Subnet Planning document (Requires Adobe Acrobat Reader)
• SubnetOnline website
• LearnToSubnet website
• 3COM website .PDF file, 40 pages, Click HERE to get to their whitepapers page, and then click on the "Understanding IP Addressing: Everything You Ever Wanted To Know" link
• IP Calculator software tool

  
  

• IP Subnetter software tool

         

• IP Address Assistant (Team Valley Software)
  

At the request of student, Chris Walter, I have posted the IETF recommended PRIVATE IP ADDRESS SCHEMES (I've copied these directly from RFC 1597)

The Internet Assigned Numbers Authority (IANA) has reserved the following three blocks of the IP address space for private networks:

10.0.0.0 - 10.255.255.255

172.16.0.0 - 172.31.255.255

192.168.0.0 - 192.168.255.255