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Hello,
  we have met the following network setup problem.
A shift of the system time to the past leads to the incorrect long sleep of
the dhclient.
Step by step reproduction:

1. obtain address via dhclient at timestamp t1;
2. shift system time  to the past to timestamp t2;
3.  bug: dhclient misses renew operation. it is sleeping in 'select' for
"lease time"/2 + (t1 - t2) seconds.

Time shift can be great, for example in setting up local time on guest
linux OSes in some hypervisors.  It consequently leads to the losing
address of the interface.

-- 

Best regards,
Vladimir Kunschikov
Lead software developer
InfoTeCS JSC