Can anybody tell me if theres any packet modification lib/utility that allows people to modify the packet at app level before sending them through NAT ?
eg. i want to change private ip returned in dns to its public equivalent.
Answers that dont work: -I dont use static mapping from priv:public realms, so theres no question of setting up another dns server with public ips. -Use cisco router.
So in short any lib/utility that goes along with iptables and allows user to modify payload of for eg. DNS packets.
I do not want to buy
The QUEUE and NFQUEUE iptables targets pass the packet to a user-mode process, which is then free to drop the packet or modify it before sending on its way. The netfilter project provides a C library to take care of getting packets in/out of the kernel for you; there are high-level bindings available too (python-libnetfilter-queue and nfqueue-bindings cater for Python and Perl respectively).
Alternatively, write a proxy to sit in front of your nameserver.