DHCPv6 support in Network Manager isn't RFC compliant

[Stéphane Graber <stgraber ubuntu com>]

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Hello,

As I'm not subscribed to this mailing-list, I'd appreciate it if you
could Cc me on your replies. Thanks


I've recently been spending quite a bit of time testing Network
Manager's IPv6 support on Ubuntu as part of our ongoing effort of
getting full IPv6 support for Oneiric.

It's really looking good and Network Manager does a great job of
handling all the possible use cases I have, except one small detail.

I noticed yesterday that Network Manager uses a different DHCP lease
file for each connection. I can understand why it's been done this way
for DHCPv4 (makes it more readable and easier to cleanup) but that's
unfortunately breaking DHCPv6 support.


You're probably aware that with DHCPv6, "host" definitions on the server
side are no longer tied to a MAC address but instead to a DUID.
This DUID is defined in RFC 3315, section 9.
http://www.ietf.org/rfc/rfc3315.txt

Quoting part of this specific section:
   The DUID is carried in an option because it may be variable length
   and because it is not required in all DHCP messages.  The DUID is
   designed to be unique across all DHCP clients and servers, and stable
   for any specific client or server - that is, the DUID used by a
   client or server SHOULD NOT change over time if at all possible; for
   example, a device's DUID should not change as a result of a change in
   the device's network hardware.

The way the ISC dhclient works, it's looking for a default-duid field in
its lease file. For example, on my machine I currently have:
  default-duid "\000\001\000\001\025\303}\370\000#\024\243\331\244";

This is fine as long as dhclient always uses the same lease file but
it's sadly not the current behavior when used with Network Manager.

The current behavior's IPv4 equivalent would be a changing MAC address
for every single network defined in Network Manager, which is really
problematic for system administrators who need to do per-host
configuration with DHCPv6.


I'd highly recommend Network Manager either uses
/var/lib/dhcp/dhclient6.leases as its lease file or if you absolutely
want to keep a separate lease file per connection, then use the
following algorithm:

 1) Check if /var/lib/dhcp/dhclient6.leases exists
  1a) If it does, grab the DUID from it.
  1b) If it doesn't, generate a new DUID and write it to
/var/lib/dhcp/dhclient6.leases
 2) Write that DUID to your per-connection lease file prior to starting
dhclient

Let me know if you have any question!

Thanks

- -- 
Stéphane Graber
Ubuntu developer
http://www.ubuntu.com
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