How to protect FreeBSD from IP spoofing ?

Tue Feb 17 06:51:03 PST 2009

Dear all.
I am a newbie of FreeBSD, would like to get alot of information about FreeBSD such as IPFW.
I am annoyed by IP spoofing but dont have any way to prevent it.
Can any one tell me how to do ?
Thanks in advance.

PS:
I am using 6.4-PRERELEASE FreeBSD 6.4-PRERELEASE.
The FreeBSD box is used for web server, and it is forwarded every parket of port 80 from LAN router.