My take on "how to learn Linux" -
http://blog.jdpfu.com/2014/12/28/learning-linux
I think you'll appreciate this, since it was written for people like you exactly. People who want to become "power-users", then admins (at some level).
Basic IPv4 network knowledge is pretty easy. There are complexities to networking that are well beyond my knowledge, but I've worked with some brilliant network designers who have forgotten more than I've ever known.
For IPv6, HE has free training.
Many universities have security programs. Some sponsor offensive security teams.
The only way to do this safely, within legal limits yourself, is to hack your own network and equipment. Virtual machines are a core part of this.
There are security conferences almost every week of the year someone in the USA. This weekend there is a conference in Nashville. There are online CTF and KotH competitions too. They provide systems and networks specifically for teams to attack.
As you will soon learn, everything you want to learn will take decades. So... like eating an elephant, start with one bite at a time.
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