[all variants] How do you learn networking from an Ubuntu/Linux perspective?

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http://ubuntuforums.org – I don't know a lot about linux or networking, though I do know the basics. I've looked at a lot of free networking materials on the net but they all seem to teach things from a windows perspective (eg, they use windows commands). Are there any kinds of free material (ebooks, courses, podcasts etc) on the web to learn networking from a linux perspective, using linux commands and linux programs? (Hardware)