DHCP, Autoipd, fallbacks, fall (forward?)

[Thomas Charron]

  Quick question for everyone, in case they've encountered a situation
like this, or know dhclient and avahi.

  So, I have a system which comes up, and there is no DHCP server
available.  Link reverts to avahi-autoipd, which assigns a link local
address.

  Is there a way I can have the system, while USING the link local
address, occasionally TRY to do a DHCPDISCOVER, and if a server is
found, go ahead and reconfigure via DHCP?

  Basically, I have a bridge set up across 3 of my eth interfaces,
which are bridged together.  The bridge is configured to use dhcp:

auto networkbridge
iface networkbridge inet dhcp
        bridge_ports console aux1 aux2
        bridge_fd 9
        bridge_hello 2
        bridge_maxage 12
        bridge_stp on

  The system is headless, and when no DHCP is found, reverting to link
local is fine.  The application running on the headless server uses
mDNS to broadcast.

  When the system is connected directly to the client PC (That's the
console interface in the above config), link local is fine, the
console also reverts to link local, as it also cannot get an address.
However I would like it if the bridge, upon somehow 'magically'
detecting it CAN get a DHCP server, go ahead and get one.  JmDNS (Java
based mDNS services, which are used within our java server) will
handle the notifications, and the console app can receive this
notification, and do what it wishes to do (reconfigure its interface).

-- 
-- Thomas