MAC address definitely doesn't survive out on the public internet. The MAC address is Layer 2, the link layer, and IP Address is Layer 3, the application layer. The destination IP address in a request stays the same through out the entire request because it is at the application layer. The MAC address portion of the tcp/ip packet, however, changes at each hop. The network devices use ARP to say, "please give me the MAC address of the device with this IP address" where the IP address is the destination of the next hop. So your computer would send out a packet and say "what is the MAC address of my router please?", the router would reply, your computer would send along the packet with the Layer 2 address set to the MAC of your router and then your router would pick it up. Then your router would ask its upstream gateway what its MAC address is (via ARP), swap out the Layer 2 address with the MAC of the upstream gateway and then send it along. In each case, what ever device is doing the routing creates a new frame for the Layer 2 info, discards the old one, and keeps the Layer 3 stuff the same.
As a side note, MAC addresses are supposed to be unique. And they generally are. However, that hasn't always been the case. I remember 3Com had problems with reusing MAC addresses in their NICs in the mid-90s when I was doing tech support, which was quite embarrassing for them and potentially quite annoying for customers. Judah On Mon, May 3, 2010 at 11:05 PM, Dana <dana.tier...@gmail.com> wrote: > > they are unique. But -- I know it's complicated, cause it took most of > the first year of the Cisco program to get it through my head -- take > my word for it, even a packet capture would only show the MAC address > if it was on the same subnet. That's not even an expert opinion, > that's a fact. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~| Order the Adobe Coldfusion Anthology now! http://www.amazon.com/Adobe-Coldfusion-Anthology-Michael-Dinowitz/dp/1430272155/?tag=houseoffusion Archive: http://www.houseoffusion.com/groups/cf-community/message.cfm/messageid:317345 Subscription: http://www.houseoffusion.com/groups/cf-community/subscribe.cfm Unsubscribe: http://www.houseoffusion.com/groups/cf-community/unsubscribe.cfm
