[Bug 974284] Re: invoking dhclient3 with -1 causes issue if no dhcp server available

[Rafi Khardalian]

The problem is actually more prevalent than just boot time.  In fact, if
the DHCP server goes away at any point and the lease expires, dhclient
will timeout and exit without ever retrying again.  The result is that
the system in question basically falls off the network, with the only
way to recover being manual intervention.  To be clear, this means
recovery requires physical access or remote management capabilities.

It's straightforward to reproduce the problem.  Configure an Ubuntu
system as a DHCP client and set the lease time on the server to
something short, like 60 seconds.  After the system has successfully
booted and grabbed an IP, shut down the DHCP server.  Within 2 minutes,
the dhcp client will timeout, lose it's IP address and drop off the
network with no chance of recovering automatically.

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https://bugs.launchpad.net/bugs/974284

Title:
  invoking dhclient3 with -1 causes issue if no dhcp server available

Status in “ifupdown” package in Ubuntu:
  New

Bug description:
  In bug 838968, we modified ifupdown to invoke dhclient3 with '-1' as a
  parameter [1], and subsequently changed the default timeout of
  dhclient in isc-dhcp3 to from 60 seconds to 300 seconds [2].

  The reason for this is that we now have a reliable "static-networking-
  up" event that can be used for upstart jobs to start on, when static
  networking is up.  Here, static is any networking with an entry in
  /etc/network/interfaces.

  That event is used by cloud-init and other things that depend on
  network.

  The fallout of this is that if for some reason a server (or cloud-
  instance, or anything really), boots and does not obtain a dhcp
  address in 5 minutes, then it will give up forever.  The previous
  behavior is that it would try forever.

  This scenario isn't terribly unrealistic.  A power fail could take out
  a dchp server, cause a fsck, while the server came up 5 minutes before
  the dhcp server was up.

  Issue was originally raised in #openstack-dev by rmk around
  2012-04-05T06:42:19 [3]

  --
  [1] http://bazaar.launchpad.net/~ubuntu-branches/ubuntu/precise/ifupdown/precise/revision/56
  [2] http://bazaar.launchpad.net/~ubuntu-branches/ubuntu/precise/isc-dhcp/precise/revision/32
  [3] http://eavesdrop.openstack.org/irclogs/%23openstack-dev/%23openstack-dev.2012-04-05.log

  Releated bugs:
    * bug 838968: static-network-up event does not wait for interfaces to have an address

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