Cisco press offers a free ebook download on their website for the book "Cisco Router Configuration, Second Edition".
Even though the book is from 2001 it offers a wealth of well written information about the basics of networking, Cisco device configuration, TCP-IP configuration. It even covers IPX and Appletalk.
Get the download from the Cisco Press website (find "Download a FREE eBook" on the right of the web page).
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