Tutorials

https://apex.oracle.com/pls/apex/f?p=44785:1:1969705861759208:::::

Interesting Oracle docs

http://www.oracle.com/us/dm/h2fy11/100047284-index-oem-1512886.html?msgid=3-5904687985

Reasonably simple explanation of subnets

http://www.techrepublic.com/article/ip-subnetting-made-easy/6089187