Help with DHCPv6 client-identifiers
Simon Hobson
dhcp1 at thehobsons.co.uk
Fri Nov 18 09:36:23 UTC 2011
<scott_stone at trendmicro.com> wrote:
>It seems that the dhcp client identifiers for DHCPv6 are
>*arbitrary*. Is there no way to know ahead of time what they would
>be, since they're not mapped to anything uniquely identifiable on
>the machine (ie, MAC address)? Do I need to have someone manually
>investigate all of these hosts to find their client identifiers or
>is there something I'm missing here...?
No, you aren't missing anything !
This is a subject that's been flogged to death in the past, but such
quaint ideas as being able to identify a device by something (more or
less) immutable* and determinable by looking at a label, such as MAC
address, isn't supported in the IPv6 DHCP protocol.
AIUI from previous threads (not got into it myself yet), there are 3
forms for the IPv6 ClientID. One of these is derived from the MAC,
but is generally only used on devices without persistent storage.
Other devices generate a unique ID on first boot and then use that -
until you switch OS or reinstall the OS.
To top it off, the MAC address (hardware) is not included.
I also understand that there is no option for specifying routers via
DHCP, though that's being reviewed ? The argument for lack of a
routers option is that it's done by router discovery protocols - but
that removes a lot of control from network admins.
In short, it would appear that no-one using these sorts of
assignments was involved in the standards setting process - or if
they were, then their input was overruled.
* Much debate about this detail.
For most modern systems, the MAC address is pretty well immutable -
it's not common to be swapping NICs, the majority are built in to the
motherboard.
The other issue is about devices with multiple NICs - eg a laptop
with wired and wireless interfaces. The argument for not using the
MAC address is that by using a Client ID it works the same whichever
interface(s) is used.
--
Simon Hobson
Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
Christmas stocking fillers. Some available as e-books.
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