packet interceptor

hello all I am looking for a sample C code for packet interceptor....

Any help is appreciated

Thank you

Google maybe?

http://www.codeproject.com/KB/IP/smfirewall.aspx C++
http://sectools.org/sniffers.html might be a C version here

this seems to be a code for firewall...but my aim is to receive a packet as it is....and parse the details and do the required changes and then forward it to my another code.....

Isn't that what a firewall does? Routers and firewalls have the same basic behavior (receive a packet; interpret the packet's source/destination information; forward the packet on). How much interpretation depends on the application.

Viggy