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

[Neil Wilson]

I would suggest that is a design flaw in your network - which is
working in an IPv4 manner, not an IPv6 one. You should have used a
prefix smaller than /64

The problem here is with the network design, not the image.

On 4 June 2014 14:40, Alex Bligh <ubuntu at alex.org.uk> wrote:
> That doesn't work if (for instance) you have 2 machines on the same SDN
> virtual LAN, which is a /64, and you want to prevent source spoofing
> between them. For avoidance of doubt, we do use /64s.
>
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> Title:
>   IPv6 Privacy Extensions enabled on Ubuntu Server by default
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Neil Wilson

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https://bugs.launchpad.net/bugs/1068756

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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