I came across this rather nicely presented tut on the basics of using Libpcap for writing your own sniffing apps


If any of you fancy learning more about using Libpcap in writing your own security apps I can highly recommend this book

"Building Open Source Network Security Tools: Components and Techniques"
Mike Schiffman
Wiley Publishing
ISBN 0-471-20544-3

I hope this info is of use to some body