On Thu, 21 Jul 2005, JC wrote: > I was hoping someone could possibly shed some light into this or at > least point me to the right direction... > > I am trying to develop a kernel module level solution for dynamic host > multihoming. This requires that I mangle packets from specific > applications running on the system right in the stack and basically > change the interface the packets are sent from (at least two > interfaces). > > I understand that I need to register my mangling function with one of > the 5 netfilter hooks (the ROUTING one?), grab the interesting packets > and change..... something in the skbuff. > > What really evades me is where/when does routing *exactly* happen. If > I know at which point it happens, I should tap right after it and > change the interface to the one I want. Or this whole idea could be > bad and I end up breaking something in the > packet and it gets dropped... At some point, I found this and squirreled it away: # .========================================================. # | PACKET PROCESSING PATH | # +========================================================+ # # Arriving Packets # ========================================================== # No. | Table | Chain | Description # ---------------------------------------------------------- # 1 | | | On the wire # 2 | | | At interface # 3 | Mangle | PREROUTING | # 4 | NAT | PREROUTING | # 5 | | | Routing descision # 6 | Mangle | INPUT | # 7 | Filter | INPUT | # 8 | | | To application # # Departing Packets # ========================================================== # No. | Table | Chain | Description # ---------------------------------------------------------- # 1 | | | From Application # 2 | | | Routing decision # 3 | Mangle | OUTPUT | # 4 | NAT | OUTPUT | # 5 | Filter | OUTPUT | # 6 | Mangle | POSTROUTING | # 7 | | | At interface # 8 | | | On the wire # # Forwarding Packets # ========================================================== # No. | Table | Chain | Description # ---------------------------------------------------------- # 1 | | | From Application # 2 | | | Routing # 3 | Mangle | PREROUTING | # 4 | NAT | PREROUTING | # 5 | | | Routing decision # 6 | Mangle | FORWARD | # 7 | Filter | FORWARD | # 8 | Mangle | POSTROUTING | # 9 | NAT | POSTROUTING | # 10 | | | At interface # 11 | | | On the wire > Of course, that needs to happen for both locally generated traffic and > incoming traffic, so that I link the incoming packets to the right > applications. Why does this sound like NAT, where you take data from one interface and spit it out on another (receive is done the same way)? Hope this helps.. - -- "There are 10 types of people in the world: Those who understand binary and those that don't."
