host-identifier with IPv6

Eustace, Glen G.Eustace at
Sun Mar 1 21:51:30 UTC 2009

> If your DHCPv6 clients follow the spec, chances are that they are
> already sending you the MAC address in the DUID option.   The server
> is encouraged to treat the DUID as an opaque field, and the DUID extra
> information in the DUID is intended to allow it to work correctly even  
> if you use the same network card at different times in different
> machines.   But on a practical level it's likely that every single
> DHCPv6 client you have is in fact sending their current Mac address
> in the DUID.   You shouldn't use the Mac in the DUID as a unique
> identifier (that is, you shouldn't ignore the additional information
> in the DUID), but if you're just trying to make an association or an
> access control decision based on it, it should work just fine.

Whilst the server may be encouraged to treat the DUID as opaque, the reality is that I have the MAC addresses (thousands of them) of all our known-clients in a database,  the NICs do not (very seldom at any rate) move around and/or change machines and I need to uniquely identify the client in order to assign its address.

It is easy to say "you shouldn't use the Mac in the DUID as a unique identifier", the reality is I have no alternative.  I cannot determine what the DUID will be in advance for any given client, yet I must do so in order to build a host definition that will allow me to allocate its correct address.  So unless I have a means to extract out and allocate the address based on the MAC, I am stuffed :-(


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