check packets for its delivery

hello,
On linux pc made as Router,when a packet is built after IP
header addded to packet I want to check whether a packet is having its
destination ip == any local internal attached networks ip.Consider
Router is having no. of NIC's that mean no. of internal networks
attached to that Router.
I am doing the C progarm for the above problem that will print that
packet is having delivery to local network.
Required hints to program above about how to crosscheck that?