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I am studying for my CCNA, and I was wondering why we can't route packets between networks with MAC addresses. Is it theoretically possible to know the location of every computer on the internet, and have switches (possibly at an ISP), that know every MAC address out there, and are able to forward it to the correct switch?

Would a system like this even be practical to implement (if IPs hadn't already been implemented)?

oli2
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1 Answers1

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Because that would mean that every node in the network would have to know every mac address everywhere

think of it like this. IP routing is like routing by postal address

123 main st,
Big City
Ohio
USA

This is structured. Post office in California (where I mail this letter) doesnt know about 'main st' at all, but it knows to send to 'Big City' sorting office. They will know

MAC address is just a random number. That would be like mailing using SSN

Imagine a letter that said simply

 354-76-8791

as the address, where would the post office send it when I mail it. They would need a registry of every SSN and where they live, updated all the time.

pm100
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  • That doesn't really answer my question. Is there any real reason why it's impossible to use MACs for routing? – oli2 Mar 08 '22 at 00:51
  • @oli2 Yes it does. Off topic. – user207421 Mar 08 '22 at 00:56
  • @oli2 it precisely answers it in the first sentence, and then uses an analogy to clarify. The important thing is that a MAC address is a random number – pm100 Mar 08 '22 at 00:57