Re: DAD question

["Fred Baker (fred)" <[e-mail]>]

On Aug 14, 2012, at 4:41 AM, Francis Dupont wrote:

> I remember (perhaps the first detected duplicate?) a very early occurrence
> before 1995 with a DEC box using a cloned full config. Same Decnet address
> so same MAC address so same IPv6 link-local address…

Where I'm coming from in this is an expectation on my part that appears to not be shared. If duplicate MAC addresses are unusual but reasonably common (happen with some probability like .01% or whatever), there's a reasonable expectation that there would be a work-around for the issue. The work-around, I suggest, would be to have the station use a privacy address instead of a MAC-based address when a duplicate MAC address is detected.

I've said before that I find the fixation an MAC addresses strange; not all devices have MAC addresses in the first place, and having built an EID from a MAC address, there is no case in which we try to derive the MAC address from it. Not all devices, believe it or not, have Ethernet or WiFi interfaces, and one with a WiFi and something else, such as your telephone, would only use the WiFi MAC address for the EID on that interface. What do I mean by "deriving the MAC from the EID"? There was a proposal in CLNS at one point (which failed for several reasons) to not need ES-IS and instead simply use the MAC address of an interface as the host identifier part of an NSAP - a router could pull it out and simply forward the datagram to the derived MAC address - and that model was used in XNS and IPX as well. But for the same reasons that OSI didn't go with that model, we have not chosen to go with that model in IPv6. 

So the MAC address is at most a seed for building an EID, one of many, and to my small mind if it doesn't result in a unique one, the obvious recovery action is to pick another by a different algorithm.

I gather nobody agrees with me.