First, don't exit when the link goes down on an interface. Instead,
teach dhclient to track changes in link state and to enter the reboot
state when the link on an interface goes up causing dhclient to attempt
to renew its existing lease.
Second, remove the change I added to clear the old lease when dhclient
exits due to an error (such as ifconfig down). If an interface is
using autoconfiguration it should keep its autoconfiguration as much as
possible. If the next time it needs a configuration it is able to reuse
the previous autoconfiguration, then leaving the settings intact allows
existing connections to survive temporary outages, etc.
PR: bin/166656
MFC after: 1 month
packets instead of allowing the protocol stack to pick a random source port.
This fixes the behaviour where dhclient would never transition from RENEWING
to BOUND without going through REBINDING in networks which are paranoid about
DHCP spoofing, such as most mainstream cable-broadband ISP networks.
Reviewed by: brooks
Obtained from: OpenBSD (partly - I'm not convinced their solution can work)
MFC after: 1 week (pending re approval)
