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Not exactly, the MAC address (which is a far stronger unique identifier than an IP address) will usually only survive the first hop in an IP transmission.

Not even 'usually', it doesn't exit your LAN at all, once it hits your router, it is stripped and your data is packed with a different MAC address on the WAN (or any other layer 2 identifier depending on your connection), same for each hop after that.

If you use EUI-64 as your interface ID in IPv6, your MAC address is part of your IPv6 address. That said, no modern OS does that anymore, times 1% of IPv6-enabled users, so the closer term is "almost never".

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