host-identifier with IPv6

sthaug at sthaug at
Mon Mar 2 20:17:25 UTC 2009

> I applaud you for your optimistic view of DHCP implementors.   Here's  
> the problem.   The Mac address *can't* be a unique identifier, because  
> it can change, either because of hardware changes or because the  
> address prom gets reflashed.   Or, on some types of hardware, because  
> there is no fixed hardware address.   But we want a stable, unique  
> identifier.   So we get our uniqueness from a combination of the Mac  
> address and the time, because it would take a fairly surprising  
> coincidence to make both of them be the same on two different nodes,  
> and then we keep that address in perpetuity.

It seems people who are asking for unique identifier are perfectly happy
with the level of stability they get with MAC addresses today, and that
you would like to remove this stability.

Yes, MAC addresses can change, for various reasons. However, in most
cases they *don't* - which makes it possible to base configuration on a
MAC address taken from a sticker on the equipment or similar.

> So like it or not, your solution has to be adaptive.   It would be  
> nice if it were otherwise, but complaining about it isn't going to  
> change it, and believe me, if there were a way to do what you want in  
> the protocol spec, we would have done it.   It's easy to postulate  
> perfect solutions in a vacuuum (say that three times fast), but you've  
> been on this mailing list and doing DHCP long enough to know just how  
> likely it is that vendors will even read the spec, much less follow it  
> if it's inconvenient.

Again, it sounds like you want to remove something that works well with
IPv4 today, simply because it is not a perfect solution. It doesn't
*have* to be perfect, it needs to be *predictable* (given for instance
a sticker with a MAC address) and *stable enough*.

Why is this difficult to understand?

Steinar Haug, Nethelp consulting, sthaug at

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