Mac address are supposed to be Globally Unique, MAC addresses are 12-digit hexadecimal numbers (48 bits in length)
–With all the pc’s in the world it would be impossible to never have a duplicate Mac address.
IP Address are not Globally Unique in the sense. A device uses a ip address for a set amount of time. the device rents or borrows the ip address for the set time then relinquishes it when complete. If the Device ever needs another ip address in the future it will re acquire which can be different from the original.
–an ip address must be unique within a network. That is why sub netting is used, an organization with more then 255pcs will need to sub net. This means the Gate way will have the network and with a series of routers the internal large network will be departmentalized into subnets (SubNetworks= Networks within networks)
IPv6 is being used by various companies all over the world. (that is all i will say about that.)
Well i Hope i helped and if anyone needs further information you can contact me at IThelp@yahoo.com i would be glade to offer my assistance with IP addresses and subnets.