Re: [dhcwg] DUID+IAID

[Jeffrey Hutzelman <[e-mail]>]

On Fri, 2012-03-30 at 06:22 +0000, Ted Lemon wrote:
> > I am not sure I understand that.  Why would the proposed hardware-addr-option
> > not identify the interface?
> 
> Because it is not an identifier.   It is a hint.   If you call it an
>  identifier, someone will start using it as one.

It is an identifier, or at least the IEEE tries fairly hard to make it
one.  It's just not an identifier that's guaranteed to be bound to
anything useful to DHCP, and especially not to the client as a whole.

Note that one reason you can't use a MAC address as an identifier _at
the protocol layer_ is because some clients will end up using the same
MAC address on multiple interfaces.  For example, until only a few years
ago, Sun boxes had a single MAC address for the entire machine, and used
that address for every interface.


> > My understanding of the proposal is that the MAC address is *added* to the request
> > as an option, so we would have both the DUID and the MAC, thus allowing us to
> > identify both the device and the interface, which is good IMO.
> 
> In principle there's nothing incorrect about this statement, but in
>  practice there is no protocol need to identify the interface.

True -- the _protocol_ has no such need.  But that doesn't change
whether the hardware address is in fact an identifier.



More importantly, the question of whether this is an "identifier" or not
is a pointless distraction from the original question, which was about
_which interface's_ hardware address the option is expected to contain.

> It's possible that you might want to use DHCP to allocate an address
>  for a tunnel endpoint, but in that case there is no physical
>  interface, and the MAC address that the relay agent will add to the
>  packet will be the address of the physical interface, not the tunnel,
>  which has no MAC address.   So this is another reason not to call this
>  an "interface identifier."   It's the MAC address of the interface out
>  which the DHCP packet was sent.


In fact, it sounds like it's exactly the source MAC address of the
packet as it was received by the relay agent.