Hi kernel experts,

Iím trying to modify the IP packet src & dest address after receiving from the wire and reconstruct the packet at kernel layer without going to apps layer and ultimately send out the packet. So, the recommended API to be used is ip_finish_output() (as it is the only exported symbol to send UDP packets). However, since the IP header content are changed, the system must automatically recalculate checksum and needs mac address as well, and most of the time mac address of unknown hosts.

Currently, when I try, I need to invoke mac address resolution via arp by manually calling neigh_lookup of existing arp entry before sending the packet by calling dev_queue_xmit().

My questions is how can I change (dest/src IP and port number) at before ip_finish_output() by accessing specific struct should I want to send the packet to unknown hosts (unknown means remote hosts that do not have an arp entry in local host's arp table) by calling ip_finish_output().

Thank you very much for your advice.