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[Launchpad Bug Tracker <1652348@xxxxxxxxxxxxxxxxxx>]

This bug was fixed in the package klibc - 2.0.4-8ubuntu4

---------------
klibc (2.0.4-8ubuntu4) zesty; urgency=medium

  * debian/patches/dhcp-one-socket-per-interface.patch: Use separate
    sockets for DHCP from multiple interfaces.  Thanks to Jay Vosburgh
    <jay.vosburgh@xxxxxxxxxxxxx>.  Closes LP: #1652348.

 -- Steve Langasek <steve.langasek@xxxxxxxxxx>  Tue, 24 Jan 2017
11:38:13 -0800

** Changed in: klibc (Ubuntu)
       Status: In Progress => Fix Released

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https://bugs.launchpad.net/bugs/1652348

Title:
  initrd dhcp fails / ignores valid response

Status in klibc package in Ubuntu:
  Fix Released
Status in klibc source package in Xenial:
  Triaged

Bug description:
  [SRU justification]
  Changes to ordering of kernel enumeration of network interfaces, which may happen in any release, can regress network configuration from an initramfs.  Support for netbooting should not depend on interface order, it should work reliably on all systems.

  [Test case]
  Detailed reproducer described in 
  <https://bugs.launchpad.net/ubuntu/+source/klibc/+bug/1652348/comments/35>.

  [Regression potential]
  Moderate regression potential, because of a relatively large patch touching a not-widely-used but still critical piece of code.  Regression testing should include verifying that MAAS-booted cloud images still work as expected in a variety of environments.

  
  Between kernel versions 4.4.0-53 and 4.4.0-57 a bug has been (re?)introduced that is breaking dhcp booting in the initrd environment.  This is stopping instances that use iscsi storage from being able to connect.

  Over serial console it outputs:

  IP-Config: no response after 2 secs - giving up
  IP-Config: ens2f0 hardware address 90:e2:ba:d1:36:38 mtu 1500 DHCP RARP
  IP-Config: ens2f1 hardware address 90:e2:ba:d1:36:39 mtu 1500 DHCP RARP
  IP-Config: no response after 3 secs - giving up

  with increasing delays until it fails.  At which point a simple
  ipconfig -t dhcp -d "ens2f0"  works.  The console output is slightly
  garbled but should give you an idea:

  (initramfs) ipconfig -t dhcp -[  728.379793] ixgbe 0000:13:00.0 ens2f0: changing MTU from 1500 to 9000
  d "ens2f0"
  IP-Config: ens2f0 hardware address 90:e2:ba:d1:36:38 mtu 1500 DHCP RARP
  IP-Config: ens2f0 guessed broadcast address 10.0.1.255
  IP-Config: ens2f0 complete (dhcp from 169.254.169.254):
   addres[  728.980448] ixgbe 0000:13:00.0 ens2f0: detected SFP+: 3
  s: 10.0.1.56        broadcast: 10.0.1.255       netmask: 255.255.255.0
   gateway: 10.0.1.1   [  729.148410] ixgbe 0000:13:00.0 ens2f0: NIC Link is Up 10 Gbps, Flow Control: RX/TX
        dns0     : 169.254.169.254  dns1   : 0.0.0.0
   rootserver: 169.254.169.254 rootpath:
   filename  : /ipxe.efi

  tcpdumps show that dhcp requests are being received from the host, and
  responses sent, but not accepted by the host.  When the ipconfig
  command is issued manually, an identical dhcp request and response
  happens, only this time it is accepted.  It doesn't appear to be that
  the messages are being sent and received incorrectly, just silently
  ignored by ipconfig.

  I was seeing this behaviour earlier this year, which I was able to fix
  by specifying "ip=dhcp" as a kernel parameter.  About a month ago that
  was identified as causing us other problems (long story) and we
  dropped it, at which point we discovered the original bug was no
  longer an issue.

  Putting "ip=dhcp" back on with this kernel no longer fixes the
  problem.

  I've compared the two initrds and effectively the only thing that has
  changed between the two is the kernel components.

  Ubuntu kernel bisect offending commit:
  # first bad commit: [fd4b5fa6e3487d15ede746f92601af008b2abbc0] mnt: Add a per mount namespace limit on the number of mounts

  Ubuntu kernel bisect offending commit submission:
  https://lkml.org/lkml/2016/10/5/308

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