James Carlson wrote: > Nicolas Droux writes: >> On Sep 4, 2007, at 8:45 AM, James Carlson wrote: >> >>> The question I'm asking here is: "why?" >>> >>> Under what circumstances does it make sense to provide this failure >>> mode for administrators? How does it help rather than hinder? >> It provides the user the ability to preserve and enforce the >> assignment of factory MAC addresses to virtual machines in a >> consolidated environment. If the administrator specifically asks for >> a factory MAC address but none are available, then the operation >> would fail. The (default) automatic mode is also there for the users >> who don't care if a random address is assigned to the VNIC instead. > > Yes, I understand what it would do. I still don't see why that's a > helpful operation. > > It clearly provides a special failure mode. What isn't clear is why > users of this feature would prefer to have the operation fail rather > than having the system provide a best attempt (perhaps with warnings) > instead. > > What are the administrators actually doing with these MAC addresses > that causes them to prefer failure? >
Factory assigned MAC addresses are inventoried entities in some companies. They keep track of the MAC address(s) the machine has along with other information (like physical location etc). Sparc's have a hostid but on x86, this is the only unique way to identify the physical machines from the packet on the network. Random MAC addresses are random at best and have no guarantees that they are unique across different machines. The virtualization crowd has adopted random mac address but a sizable set of customers are still skeptical about duplication etc. A user assigned MAC address is cumbersome at best and some customers are not prepared to pay the overheads of assigning them and tracking them across their data center(s). As such, the NIC which have multiple factory assigned MAC addresses becauses a very useful resource for a set of customer wanting to play in virtualization space (but not caring about live migration - specially zones). They don't have to deal with user assigned addresses or random addresses and they can inventory the factory assigned mac addresses just as they used to before. Yes, they get limited by the number of VNIC they can create but 8-16 factory assigned mac address gives them sufficient headroom to play. Thats why you need to either use the 'auto' flag where you don't care but if user specified factory, then he does care and we can't get him a factory mac address, we fail the operation. Perhaps there is a better administrative interface to express this and we are open to suggestions. But hopefully you get the idea what we are trying to achieve. On a different note, having examples is always very helpful. Cheers, Sunay -- Sunay Tripathi Distinguished Engineer Solaris Core Operating System Sun MicroSystems Inc. Solaris Networking: http://www.opensolaris.org/os/community/networking Project Crossbow: http://www.opensolaris.org/os/project/crossbow
