network interface monitoring?

[Yousif Hassan]

Net-gurus:

I hope this is the right list to write to regarding this question (feel
free to redirect me to ports@ if that sounds more appropriate).

I'm looking for a facility to automatically detect network interface
carrier state changes (a network cable gets plugged/unplugged; a
laptop's wireless button gets turned on/off; etc.) and then to run a
user script on it.  The use case, fairly obvious I guess, is to execute
ifconfig and/or DHCP commands upon carrier detection; this will make my
laptop that much more useful. ;)

NetBSD has ifwatchd - which seems perfectly designed for this use case:
http://www.freebsd.org/cgi/man.cgi?query=ifwatchd&apropos=0&sektion=0&manpath=NetBSD+4.0

ifwatchd has not been ported to FreeBSD - does FreeBSD have anything
similar?

I can't imagine I'm the first to ask this question; it seems almost
everyone with a laptop would want this.

Thanks for your time/attention...!
(please CC me as I am not subscribed here)

--Yousif