The lecture course "Internet Security I" gives a detailed introduction into Internet Technology. It explains the function mode and architecture of Internets and Intranets and discusses important Internet protocols like IP, TCP, UDP, ICMP, as well as Internet addressing and DNS. Moreover, the Internet Protocol Next Generation - IPv6 - will be introduced. Furthermore important Internet services like WWW, email, ftp, telnet, rsh and more will be treated. Encryptions standards like IPSec show possibilities for information security. New techniques like LDAP and Multimedia applications will complete this lecture about Internet Technology. The lecture course provides the basic understanding for a discussion of security weaknesses of Internet and Intranets and possible targets for attacks over the Internet which will be treated in the lecture course "Internet Security II - Weaknesses and Target".