If I want to understand how does internet work,all about networking and network security,whichbooks are best to read?please refer me to good books only.
thank you

OReilly makes the best books on just about any computer topic.

O'Reilly - Designing Large-Scale LANs
O'Reilly - Network Security Assessment 2nd Edition Nov 2007
O'Reilly - TCP IP Network Administration
O'Reilly - Internet Core Protocols The Definitive Guide
O'Reilly - TCP IP Network Administration 3rd Edition
O'Reilly - The Network Administration Guide

And more.....

omg.Can anyone suggest me only about two books?like 1 book for tcp/ip one for security ? :/

Computer Networks (4th Edition ) by Andrew S. Tanenbaum, ISBN-10: 0130661023 is a good Advance Book for Networking,

Network Security Fundamentals, ISBN-10: 1587051672 is a Good Network Security Book from CISCO.

TCP/IP for Dummies, ISBN-10: 0470450606

Agreed, Tannenbaum's books are best. Boring, but good. Its a course textbook for me,

Ive got third edition. The newest (5th?) edition covers wifi and stuff, gets rid of some obsolete stuff