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stevens - 2012 - tcp ip illustrate volume 1 2nd edition
Extremely clear and exemplified.
Gives due emphasis to the key points.
Great first book.
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dostalek - 2006 - Understanding tcp ip
Explains the most important Internet protocol suite protocols deeply.
Might not be the best first TCP IP book because it is a bit advanced, but it is a very good second one once you know the basics.