Darknet - I2P

I’m not a network security specialist but sometimes I’m curious about some topics and I like to test how they work. Quite often I read in the news about darknets, recently the focus was on Silkroad and the ToR network. What is a darknet? “A darknet is an anonymizing network where connections are made only between trusted peers” - http://en.wikipedia.org/wiki/Darknet_(file_sharing) I2P is one of those darknets that I wanted to test today.