Packet interception / Mangling

[cole at opteqint.net]

Hi

I wanted to know if there are any libraries similar to pcap to intercept
packets/mangle packets.

What im trying to do specifically is like link compression, and I would then
need to check if the packet is then compressed and decompress, and so forth and
so on.

I would like to avoid having to use a ipfw divert to a port, and specifically
check all traffic to the box using a library function or some kind of hook into
the kernel.

The FreeBSD version I will be using is 4.9 or 4.11, and would like to know if
there are any such routines available, and whether it could be a userland
daemon, or if i am going to need to write a kernel loadable module?

If anyone has any ideas or suggestions, or knows anything about this, it would
be a great help.

Regards
/Cole