IP addresses are not generally globally unique (consider all the home 
routers that do local NAT (network address translation) - they all use 
the same 10 or so IP addresses on their LAN).

MAC addresses OTOH, (hardware address in network card) are globally 
unique.

On Wednesday, November 20, 2002, at 01:15  PM, Bruce ONeel wrote:

> Aren't ethernet addresses unique?  Course that requires
> an ethernet card and some way to read the address.
>
>
> "Norton, Chris" <chrisn at Kronos.com> wrote:
>> Hi Cees.
>>
>> You wrote: "UUID's shouldn't be big random numbers, they should be
>> *provable* universally unique. At the moment, the only *provable*
>> universally unique scheme that is standardized is to have the 
>> machine's IP
>> address, the process id, the current time and a sequence number in 
>> it."
>>
>> You make good sense in your analysis of UUIDs, but I'd like to point 
>> out
>> that IP addresses are not necessarily unique either.  In my company, 
>> for
>> example, the I.S. department is always messing around with those 
>> things
>> (causing endless problems for me).  On many occasions I have 
>> discovered that
>> there are 2 (or more!) machines on our network that have the same IP
>> address!
>>
>> So, while I agree that the IP address is a good starting point, I 
>> think the
>> current date/time as well as the process ID would probably also be 
>> needed
>> for uniqueness.
>>
>> I'm not an expert in such things, but I have been bitten by this 
>> problem a
>> few times in my career.  ;-)
>>
>> Cheers,
>>
>> ---==> Chris
>