Re: fixed ipv6 address with DHCPv6

[Gene Czarcinski <gene czarc net>]

See my reply to dcbw on the dnsmasq-discuss mailing list.

Gene


On 02/08/2013 12:20 PM, Pavel Simerda wrote:
> ----- Original Message -----
> > From: "Gene Czarcinski" <gene czarc net>
> > For some time I have been having a problem attempting to have a
> > dnsmasq
> > server provide a system with a fixed IPv6 address.  Setting an IPv4
> > address and identifying the system with its NIC's MAC address.  But,
> > with DHCPv6 there is no relationship defined in the standard for
> > DHCPv6 to use the MAC.
> Correct. It's replaced with UUID.
>
> > I tried using the system's name but that has not proven reliable.
> > When
> > the system and the dnsmasq server get "out of sync", it takes manual
> > intervention to correct things.  When things do work, it works fine.
> System's name is generally considered unreliable due to possible collisions.
>
> > I looked into using the Client-ID but that "number" is based on the
> > MAC plus time and will vary unpredictably.
> This has been already fixed by dcbw after long talks with me and cyphermox.
>
> > Suddenly (like yesterday) I found what appears to be the solution and
> > it is likely to have been there for some time.  By default, dhclient
> > will use LLT (Link-Layer plus Time) to define its DUID (Client-ID).
> We are switching to DUID-UUID from /etc/machine-id reportedly required by D-Bus (even though I can't image any reason as D-Bus is not commonly used over the network).
>
> > But, there is an command-line override which can change this to LL
> > (Link-Layer) which uses the MAC prepended with 0:3:0:1.
> This was the solution I originally proposed but...
>
> 1) It has some drawbacks.
>
> 2) You don't need it for normal operation. DUID-LLT saved in a disk file is stable enough for day-to-day operation. This has been solved by cyphermox even before we switched to machine-id.
>
> > The important info is here:
> > http://tools.ietf.org/html/rfc3315#section-9.4
> See:
>
> * http://tools.ietf.org/html/rfc6355 for the DUID-UUID (in the form of /etc/machine-id).
> * https://bugzilla.gnome.org/show_bug.cgi?id=691885
>
> > Also examine the dhclient man age and scroll down to "*-D*/ LL or
> > LLT/"
> I admit that DUID-LL is still better than non-stored DUID-LLT but DUID-UUID proves to be a better match that the two of those. If you have specific needs, you can still override the DUID manually.
>
> > I then did a quick (two line) patch to NetworkManage
> > [src/dhcp-manager/nm-dhcp-dhclient.c] to hardcode the addition of
> > "-D",
> > "LL" to the command-line if it is "-6".  It works as advertised.
> Thanks for your effort but unless there's a very good reason to use DUID-LL, we're not going to do that (but you can still override the actual DUID e.g. by a script).
>
> > While this works for me, I do not propose that this be the solution
> > in NetworkManager.  Instead, I propose that the default remain the same
> > and a new configuration file parameter be added: DUID= which will have
> > only two valid values: LL or LLT.
> As UUID is now the default, this proposal is obsolete.
>
> > If DUID= is not specified then the default is LLT.
> >
> > Once this is accepted and part of NetworkManager, I will update
> > network-manager-applet so the the DUID value can be specified when
> > defining an IPv6 interface.  Initially, editing the configuration
> > file should be adequate.
> Do you have any questions or arguments for still supporting DUID-LL when we have DUID-UUID?
>
> Cheers,
>
> Pavel