DHCP: renewal when cable is plugged out/in

[arnout at mind.be (Arnout Vandecappelle)]

 Hoi,

 I have an RTEMS-based system which normally is not connected to the
(Ether)network, but occasionally a user comes a long and plugs in a
cable.  I need DHCP to get a new address whenever the network cable is
plugged in, even if it's previous lease hasn't expired yet.  I also need
DHCP to fall back to a statically configured address if no reply comes.

 My questions:
 * does anyone have these features already?  I expect not, so
 * any suggestions on how to implement the network cable plug-in
detection?  My Ethernet driver detects cable (dis)connects, how should
these be propagated to the DHCP task?
   - By setting the struct ifnet's if_flags and have the DHCP task poll
on them; or
   - by sending an event to the DHCP task; or
   - by configuring a hook similar to the network taps, and having the
DHCP task register a function to it; or
   - by calling BSDnet's if_down() from the driver, make the DHCP task
listen on the routing input socket.

 I guess the last option is the best, but it requires a bit of BSDnet
insight...

 And one final question: is it OK to make changes to BSDnet itself, or
is that to be avoided because it makes tracking the real BSDnet
development more difficult?

 Regards,
 Arnout

-- 
Arnout Vandecappelle                     arnout at mind be
Senior Embedded Software Architect       +32-16-286540
Mind Embedded Development (an Essensium division)