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You seem to have a good grasp of a lot of concepts in networking and can argue cases as well as question them too. I'f your working in a networking role at the moment there's two options, carry on and hope you end up being offered a job more in your taste i.e. security. If not you can improve your odds by taking a course or qualification and then seeing if they will let you do security based roles.
For pen-testing specifically you will need to do a qualification at least, not only for your sake but to keep your employer's happy that you are in line with current regulations and standards. This is for insurance purposes mainly, a lot of hacker's who move into pentesting do not fully understand the amount of insurance you need as a pentester (especially if working freelance).
You need a mixture of theory as well as practical knowledge and experience. You could maybe speak to someone about it who is in network security, that's probably the best advice I can give you. Setup a virtual network at home using virtualbox or VMWare then try pentesting it. There are plenty of iso's about to make a decent challenge out of it. If you struggle to find a challenge look at old wargame iso's to pentest.
EDIT: congrats mandi on breaking 100 posts :)
Hey guys thanks for some tips, I recently aquired the CEH course material to start up a new carrer path. Working as a developer now, i do lack on the network admin knowledge side of things but I figure if i start now, on the side of dev, in a few years i might be able to realisitcally move into this field. But there is A LOT to learn!