Nice "d0ppelg@nger" ...
great link .. i also find site which has related with IP Spoofing .
For example, if I have the account "ray" on two hosts, alpha.gatech.edu and beta.gatech.edu, I can create a file named ".rhosts" in my home directory on beta containing the line "alpha.gatech.edu ray". This says that the user "ray" on alpha.gatech.edu may rlogin as "ray" on beta.gatech.edu without entering a password