Using netgraph for filtering/modifing packets

[James Housley]

For testing of a product I would like to be able to modify or even drop
packets based on their content.  What I have in mind is forcing the
packets through a firewall that would redirect all packet to a netgraph
node that would either pass unchanged, drop or change the contents to
assist in testing some corner cases in the code.

1) is this something doable with netgraph, I believe it is.

2) what might be a good place to start?  Have done some searching, but
haven't found any example code I thought I could start from.

Thanks,
Jim

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