Avoiding natd overhead

[Vlad Galu]

On 10/22/06, Vladimir Grebenschikov <vova at fbsd.ru> wrote:
> В сб, 21/10/2006 в 16:08 -0600, Brett Glass пишет:
> > At 03:54 AM 10/21/2006, Vladimir Grebenschikov wrote:
> >
> > > 1. use PF for nat - it does aliasing in kernel space
> >
> > True, but it doesn't let me translate the packets and
> > then continue processing within the firewall -- which
> > is necessary if you want to catch unregistered destination
> > addresses BEFORE translation and then unregistered source
> > addresses AFTER translation.
> >
> > > 2. use in-kernel libalias implementation
> > >    (I guess man-page for ng_nat(4) will help)
> >
> > Same problem. I don't know how I could send packets
> > through a Netgraph node in the middle of processing
> > by IPFW and then bring them back at the next rule.
>
> Some years ago, I've managed to use ksocket interface to catch divert
> packets from ipfw and even return them back (surprisingly it did support
> divert AF).
>
> But, be careful, it is easy to get infinite loop in kernel with this
> technique. Probably some loop prevention appears in from these times,
> but I am not sure.

   Yes, one can use mbuf_tags(9) to prevent loops.

>
> > I suppose that one solution might be, for lack of a
> > better term, a "kernel divert socket," which would
> > pass packets through a kernel module rather than a
> > user process. (This could actually be used to speed
> > up many things for which the current "userland"
> > divert sockets are now used.) It would then be
> > possible to make a "nat.ko" module, and either
> > provide a utility to control it or roll that
> > functionality into ipfw(8).
> >
> > --Brett
> >
> --
> Vladimir B. Grebenschikov
> vova at fbsd.ru
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