Cisco Internetworking Handbook
This hand book is available free. It provides a comprehensive primer on all areas of networking, the various protocols, extensive wireless data and a whole lot more.
Anyone looking for a good general introduction to anything and everything to do with networking would be hard pressed to find a more encompassing paper than this one from Cisco. It explains things in a straightforward manner that can help novices gain a foothold into the sometimes esoteric world of networking