Intercepting a packet, changing it and re-injecting into the network

[Brooks Davis]

On Fri, Dec 22, 2006 at 12:43:29PM -0300, Fabr?cio Barros Cabral wrote:
> Hello everybody!
> 
> I'm developing a network application which needs *to intercept* a packet
> (not just *copy* a packet, like libpcap does), move this packet into my
> application (userland), do some checking in the packet and according
> with some heuristics, the application may change the payload and
> re-inject the modified packet into the network. Note that sometimes,
> I'll change the payload, drop the packet or just let it go.
> 
> So, how can a I do that in FreeBSD? I can use 6.1, 7.1, any version.

The feature you're looking for is divert(4) sockets.  You use IPFW to
decide which packets to divert to userland and can reinject them as
needed.

-- Brooks
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