netgraph question : how to intercept incoming IP packets of a certain type?

[Aziz KEZZOU]

Hi folks,
Here is what I want to do : "Intercept all incoming IP packets on an
Ethernet interface of a certain type (e.g RSVP) and call my own
function to process, all inside the kernel"

Netgraph nodes : ng_iface, nf_bpf (and probably ng_ether) look
promising for this task but I can not figure out how to do it in
practice...
 
Any help is appreciated. Thanks,

neo