[Bug 1068756] Re: IPv6 Privacy Extensions enabled on Ubuntu Server by default

[Scott Moser]

given "RFC4941 SHOULD (RFC capitalisation) be turned off by default" above, and the general lack of value of privacy extensions being enabled on a server or cloud geust, i really think we should:
 a.) turn off privacy extensions on cloud-images for 14.10+
 b.) look for a way to disable them by default for 'sever' for 14.10+
      note, this has been difficult in the past to set "server specific config". as determining what is a server and what is not is not as straight forward as it may appear. 
 c.) document how the user can use user-data to customize the file on any ubuntu guest
 d.) document how cloud provider can use vendor-data to customize this change this defualt on any ubuntu guest.
 e.) change cloud-init metadata requests to IPV6_PREFER_SRC_PUBLIC
 f.) consider this change in 14.04 for cloud-images.

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Title:
  IPv6 Privacy Extensions enabled on Ubuntu Server by default

Status in “cloud-init” package in Ubuntu:
  New
Status in “procps” package in Ubuntu:
  Confirmed

Bug description:
  Ubuntu 12.04 LTS and Ubuntu 12.10 server images both ship with the
  IPv6 Privacy Extensions enabled (as defined in RFC 4941[0]). Not only
  are they enabled, but these addresses are preferred over addresses
  obtained using SLAAC. While is may be considered a reasonable default
  on an image being used on a personal computer, it's not something that
  is sane to have enabled by default in a server environment. Having
  this extension enabled can wreak havoc if you are expecting a specific
  IPv6 address when you know the MAC addresses of your systems
  beforehand.

  The file that is responsible for causing this to be defaulted to
  enabled is: "/etc/sysctl.d/10-ipv6-privacy.conf". This file appears to
  be part of the procps package (as per the output of 'dpkg -S') and
  contains the following:

      # IPv6 Privacy Extensions (RFC 4941)
      # ---
      # IPv6 typically uses a device's MAC address when choosing an IPv6 address
      # to use in autoconfiguration. Privacy extensions allow using a randomly
      # generated IPv6 address, which increases privacy.
      #
      # Acceptable values:
      #    0 - don’t use privacy extensions.
      #    1 - generate privacy addresses
      #    2 - prefer privacy addresses and use them over the normal addresses.
      net.ipv6.conf.all.use_tempaddr = 2
      net.ipv6.conf.default.use_tempaddr = 2

  In short, IPv6 privacy extensions should not be enabled by default
  when deploying an Ubuntu server image. In a server environment you
  should be able to reliably determine your IPv6 address based on the
  MAC address of the system.

  Thank you for taking the time to look in to this as well as consider
  changing the default behavior of Ubuntu server.

  -Tim Heckman

  [0] http://tools.ietf.org/html/rfc4941

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