Can my MAC address be identified by a web site when I access the site? Does it make a difference if the site requires me to upload files?
In general it is not possible for a web site that you access to learn your MAC address. However there are special cases where the server could learn your MAC address:
- IPv6 supports assigning addresses in a way which embed the MAC address in the IP address. For privacy reasons this way of assigning IPv6 addresses is not very common.
- If you are directly attached to the same network segment as the web server, it will be able to see your MAC address. (But this is probably not the scenario you had in mind.)
- I have seen some ISPs embed the MAC address of the customer's equipment in reverse DNS records (the format was
x1-6-followed by the MAC address).
No, a remote site will only learn what public IP address you're using, not the MAC address of your device, unless you're using IPv6 with a EUI-64 address. In that case, your MAC address could be derived from the IPv6 address.
You should study the OSI Model. MAC addresses are layer-2 addresses in a frame, but frames are stripped off at a router. IP addresses are layer-3 addresses in the packet. Only packets will cross a router.
Hosts and switches use MAC addresses in the frames to deliver frames to the correct host (including a gateway, which is just another host on layer-2) on a LAN. When a gateway (router) gets the frame from a host, it strips off the frame header to get to the packet, and it routes the packet based on the IP address. When the router sends the packet out the new interface, it will create a new frame encapsulation for the new link, using its own MAC address for the new frame. As a packet moves from router-to-router to its final destination, the only surviving source MAC address will be that of the final router.