Hi every one,Can any one tell me the difference between IPv4 and IPv6.
That is a huge topic. It would probably be best to do a little background reading, then come back if you have specific questions related to pfSense.
To get you started:
IPv6 Comparison with IPv4: http://en.wikipedia.org/wiki/IPv6#Comparison_with_IPv4
IPv4 and IPv6: A Comparison: http://www.myitforum.com/articles/1/view.asp?id=6720
Side-by-Side Difference: http://www.techsutram.com/2009/03/differences-ipv4-vs-ipv6.html