Cisco is at the forefront of Internet Technology and their books are easily amongst the best written and illustrated on this subject. I have known of this particular publication for some time but its new price was well outside what I could reasonably afford. As a secondhand book it can become a real bargain, which is what influenced me to buy this copy. Buying secondhand is always risky because you cannot be certain as to its true condition and you have to be guided by the seller's description of its condition. Externally the book looked in excellent condition for the year but inside I found a few pages had been liberally annotated by a previous owner using a fine black felt pen. Underlines and comments in the margins and on diagrams were found on a dozen or so pages. Also, a few pages has yellow highlighting across certain words, phrases and headings. I would never treat a text book of this quality in this fashion so I was determined I would try and repair some of the damage. All of the black ink marks were easily eradicated using white correction fluid to obliterate the comments. I can do nothing to eradicate the highlighting, which I will have to live with. But none of these marks, although very annoying, damaged the book beyond use. It is perfectly readable. For this reason I have awarded 5-stars for the book, which I am very pleased to have obtained at long last and a knockdown price. I doubt you could buy a better reference book.