Jette Goldie wrote:
> On Sat, 30 Sep 2006 16:49:19 GMT, Duane Arnold wrote:
>
>
>>"Jette Goldie" <bosslady@scotlandmail.com> wrote in message
>>news:1vn85ksiuz92m.16q1rgqxl8v3e$.dlg@40tude.net ...
>>
>>>I have two working PCs with the same MAC address!
>>>How do the packets figure out which computer to go to?
>>>
>>>I have been travelling with two computers for weeks now staying at some
>>>German hotels whose wireless ISP sync with the MAC address of the
>>>wireless
>>>cards on my computers so I used MacMakeUp to make both computers have the
>>>same MAC address as I get my home email on my home PC and I get my work
>>>email on my work PC. Up until today, I was careful to boot only one
>>>computer at a time.
>>>
>>>I'm currently in a hotel in the UK which has free wireless to any MAC
>>>address and I forgot to reset the MAC address on the second PC back to
>>>the
>>>original. Both computers seem to be working wirelessly.
>>>
>>>How can that be?
>>>
>>>How can I have two working PCs with the same MAC address?
>>>Why don't the packets get confused as to which computer to go to?
>>>
>>
>>It's because a NAT device such as a router is being used. The router has a
>>DHCP server that issues an unique IP to each NIC requesting that an DHCP
>>IP
>>be issued to it.
>
>
> Hi Nat,
> Does this mean that each computer gets TWO unique addresses?
> The MAC and the IP.
>
> Are you saying that even though the MAC address is the same, that the
> combination of Mac + IP address is different because the IP addresses are
> different?

What I am telling you is that NAT router knows from what internal LAN IP
data is coming from and knows where to send the data back to the LAN IP.

http://computer.howstuffworks.com/nat1.htm

The MAC comes into play for the DHCP server on the router to assign an IP to
a MAC. I don't think it matters if a same MAC is in the DHCP table, as the
router is applying other things in the identification as to who is who.

Since the router has built in swicth technology, then the MAC comes into
play in broadcasting the data directly to a NIC's MAC. Otherwise, it may be
broadcasting traffic to the duplicate MAC(s) acting as a dumb hub sort of
speaking where the LAN IP has to be coming into play. There could be traffic
collision on inbound and outbound traffic for the two machines due to the
simple broadcasting of data to them as a hub, instead of finding the MAC
that the data belongs too acting like a smart switch.

http://www.homenethelp.com/web/expla...d-switches.asp

How else is the traffic making it back to the machines if the machines have
two NIC's with the same MAC(s)?

Duane :)