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

[James Troup]

Neil Wilson <neil at aldur.co.uk> writes:

> No the IPv6 system prefers privacy addresses over standard addresses if not
> explicitly told otherwise.
>
> Server *userspace software* should tell the system explicitly what it wants
> to do so that clients can connect to it.

You keep asserting this but don't back it up in any meaningful way.
It's turning this bug into a rather useless episode of "did", "didn't",
"did", "didn't".

> The problem is with the userspace software, not the IPv6
> configuration. It should be selecting addresses that it requires. Much
> outbound server software can benefit from privacy addresses and your
> solution denies them that option because of faulty binding in the
> userspace software.

I'm sorry but I don't believe the vast majority of server owners care
about the privacy of the MAC address of their servers.  Clients
(generally speaking) map directly to an individual (i.e. human being),
servers (generally speaking) don't.

> So I disagree. The problem is userspace software not using the 'hint'
> IOCTL in IPv6 address binding to tell the operating system what type
> of addresses it requires.
>
> In other words IPv4 thinking in an IPv6 world.

No, sorry, it's called being realistic and pragmatic.  If the vast
majority of software is "doing it wrong"¹, then privacy extensions
should be turned off on the server until a reasonable subset of software
is "fixed".

-- 
James

¹ And I don't think that's actually a given but let's run with it for
  the sake of argument.

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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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