The dhclientconf(5) man page says:

  The retry statement

    retry time;

  The retry statement determines the time that must pass after the client
  has  determined  that  there  is no DHCP server present before it tries
  again to contact a DHCP server.   By default, this is five minutes.

But after my machine booted, /var/log/syslog shows concerning dhclient:

Nov 17 13:24:46 ypig dhclient: DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 8
Nov 17 13:24:54 ypig dhclient: DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 16
Nov 17 13:25:10 ypig dhclient: DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 19
Nov 17 13:25:29 ypig dhclient: DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 11
Nov 17 13:25:40 ypig dhclient: No DHCPOFFERS received.
Nov 17 13:25:40 ypig dhclient: Unable to obtain a lease on first try.  Exiting.

i.e. dhclient exited instead of retrying after 5 minutes (and because
of that, I lost one hour to go to my lab to restart the network with
a "ifup eth0").

This bug is reproducible, even if I uncomment the retry line of the
/etc/dhcp/dhclient.conf file to have:

retry 60;

A working workaround is to set "timeout" to a huge value.

Either the "retry" feature or the documentation should be fixed.

for me the bug described here (#698373) effectively
is a duplicate of this bunch of errs:

bugs.debian.org/cgi-bin/bugreport.cgi?bug=695906
bugs.debian.org/cgi-bin/bugreport.cgi?bug=696642
bugs.debian.org/cgi-bin/bugreport.cgi?bug=701884

at least the net effects for #698373 have been fixed by the
fixes above.

Dear submitter,

as the package isc-dhcp has just been removed from the Debian archive
unstable we hereby close the associated bug reports.  We are sorry
that we couldn't deal with your issue properly.

For details on the removal, please see https://bugs.debian.org/1143544

The version of this package that was in Debian prior to this removal
can still be found using https://snapshot.debian.org/.

Please note that the changes have been done on the master archive and
will not propagate to any mirrors until the next dinstall run at the
earliest.

This message was generated automatically; if you believe that there is
a problem with it please contact the archive administrators by mailing
ftpmaster@ftp-master.debian.org.

Debian distribution maintenance software
pp.
Thorsten Alteholz (the ftpmaster behind the curtain)