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

[Tim Heckman]

I don't think you are correct. Here's why: the comments in the file
mentioned in my original bug report (of which I actually included the
full contents of the file) state the following:

'2 - prefer privacy addresses and use them over the normal addresses.'

Heavy emphasis on the word prefer. These addresses will be preferred for
*ALL* IPv6 traffic. This means that for all outbound IPv6 traffic,
unless explicitly bound, it will use the privacy extension address.
Which is correct, this is what software *should* do. In addition to
that, addresses brought up with privacy extension enabled are global
addresses. So even if said software were to bring use the 'global'
address they would get the privacy extension address as it is preferred.
The kernel is working right, the software is working right, the bug is
that the server image has this enabled by default.

So in short, you're absolutely wrong. The server image should not have
this enabled, and the software that is communicating over IPv6 is doing
*exactly* what it should. It's using the preferred IPv6 address.

I'm okay with this being enabled for desktops, but it has *no* place in
server environments.

-Tim

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

Title:
  IPv6 Privacy Extensions enabled on Ubuntu Server by default

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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