[Bug 1621507] Re: initramfs-tools configure_networking() fails to dhcp ipv6 addresses

[Steve Langasek]

WRT regression potential:

 2) In at least some cases, DHCP network configuration shifts from
klibc's ipconfig to isc-dhcp-client's dhclient. This should be of
minimal risk, as isc-dhcp-client is in very very widespread use. In the
event of a regression, network boot would fail, but the prior kernel
should still be bootable.

It is in widespread use; and the set of functionality used by ipconfig
in the initramfs is very small, so unlikely to run into any problems as
a result of behavior differences between ipconfig and dhclient.

However, the risk is non-zero, and I consider it acceptable to change
the dhcpv4 client from ipconfig to dhclient in SRU solely because we
should also plan to solve 1) in the longer term, which is only possible
by removing klibc-utils completely from the initramfs.  Were this not
the case, the preferred safer path would be to continue using ipconfig
for ipv4 and use dhclient only for ipv6.

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https://bugs.launchpad.net/bugs/1621507

Title:
  initramfs-tools configure_networking() fails to dhcp ipv6 addresses

Status in MAAS:
  Confirmed
Status in initramfs-tools package in Ubuntu:
  In Progress
Status in isc-dhcp package in Ubuntu:
  In Progress
Status in klibc package in Ubuntu:
  New
Status in open-iscsi package in Ubuntu:
  Fix Committed
Status in initramfs-tools source package in Xenial:
  Fix Committed
Status in isc-dhcp source package in Xenial:
  Fix Committed
Status in klibc source package in Xenial:
  New
Status in open-iscsi source package in Xenial:
  Fix Committed
Status in klibc package in Debian:
  New

Bug description:
  initramfs' configure_networking function uses ipconfig to configure the network.
  ipconfig does not support dhcpv6.  See: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=627164

  Related bugs:
    * bug 1229458: grub2 needed changes
    * bug 1621615: network not configured when ipv6 netbooted into cloud-init

  [Impact]

  It is not possible to netboot Ubuntu with a network-based root
  filesystem in an ipv6-only environment.  Anyone wanting to netboot in
  an ipv6-only environment is affected.

  These uploads address this by replacing the one-off klibc dhcp client
  (IPv4-only) with the defacto standard isc-dhcp-client, and thereby
  provide both ipv6 and ipv4 DHCP configuration.

  [Test Case]

  See Bug 1229458.  Configure radvd, dhcpd, and tftpd for your ipv6-only
  netbooting world.  Pass the boot process an ipv6 address to talk to,
  and see it fail to configure the network.

  [Regression Potential]

  1) This increases the uncompressed initramfs size by approximately 500KB, since isc-dhcp-client is added, but klibc is still needed for some other things, and is therefore present.  On systems with a very small /boot partition, this could result in failure to upgrade the initramfs.
  2) In at least some cases, DHCP network configuration shifts from klibc's ipconfig to isc-dhcp-client's dhclient.  This should be of minimal risk, as isc-dhcp-client is in very very widespread use.  In the event of a regression, network boot would fail, but the prior kernel should still be bootable.

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