On 5 March 2011 07:38, Ken Wesson <kwess...@gmail.com> wrote: > On Fri, Mar 4, 2011 at 8:07 PM, Christopher Brown <cjbrown...@gmail.com> > wrote: >> It will always return a MAC address, but in a virtualized environment those >> are a fiction and under the control of the VM creator (and hence, not real >> physical hardware). >> >> Since those MAC addrs are only required to be unique within the L2 domain, >> two separate "private clouds" in the same organization, routable at L3 but >> in separate L2, can have VMs with conflicting MAC addrs. >> Admittedly, it's a nit to pick, but who would want to debug that? > > Define "L2 domain".
e.g. an ethernet network. Machines that are directly connected to each other (possibly via a bridge/hub/switch). Somewhere where "ARP" makes sense. If you have something like this: [A]---[B]---[C] where "B" has two network cards and is an IP router. Then (A-B) and (B-C) would be two separate layer 2 domains. A and C could have the same MAC address without any confusion, because layer 2 traffic can't get from one side of B to the other. For that you need layer 3 (e.g. IP), where the IP packet would be removed from the ethernet frame when received by B and then encapsulated in a new ethernet frame before sending it on its way. A and B's left interface would have to have different MAC addresses, as would B's right interface and C. > Of course, if you consider cases like this, there can *be* no > sure-fire way to generate a node-unique number. IP addresses are right > out, thanks to local network addresses like 192.168.1.1. There must be > millions of machines out there that think their name is 192.168.1.1 in > particular. :) > > MAC address probably gets you as close as you can get without having > manually-assigned node IDs, or requiring every node have a domain name > registered (yum! expensive! Verisign would love that suggestion!) :) Well, MAC address and IP address together would get you closer, and probably close enough. Is 22 bytes short enough? :) -- Michael Wood <esiot...@gmail.com> -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
