I'm not exactly sure what you want to do, but here are some pointers that might help:
/etc/network/{if-down.d, if-post-down.d, if-pre-up.d, if-up.d}
If what you want is dhcp specific, you might be interested in /etc/udhcpc/* (but I'm not sure I would recommend this direction as you never know if a user, or TurnKey will change the dhcp client).
I hope the above helps.
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Depends what you want to do
I'm not exactly sure what you want to do, but here are some pointers that might help:
/etc/network/{if-down.d, if-post-down.d, if-pre-up.d, if-up.d}
If what you want is dhcp specific, you might be interested in /etc/udhcpc/* (but I'm not sure I would recommend this direction as you never know if a user, or TurnKey will change the dhcp client).
I hope the above helps.