pfil_add_ihook() with PFIL_IFNET

[Peter Skvarka <ps%softinengines.com@localhost>]

Hello,

I am reading man page for pfil_add_ihook() and my question is:
when I create hook with parameter PFIL_IFNET what actions should invoke 
hook with PFIL_IFNET_ATTACH or PFIL_IFNET_DETACH ?

For example when I create hook with PFIL_IFADDR then it is called on 
ifconfig iface_name up/down or on plugging/unplugging ethernet cable, or 
on other event which assigns/removes address.
Which actions invokes events PFIL_IFNET_ATTACH or PFIL_IFNET_DETACH ?

Peter