> Couldn't you simply put the next hop's MAC address (instead of IP address) into the routing table and be able to route packets just as well, with a lot less c

> Couldn't you simply put the next hop's MAC address (instead of IP address) into the routing table and be able to route packets just as well, with a lot less complexity? Several others have already answered your question -- the key points being "the OSI model" (e.g., layer 2 vs. layer 3) and the multitude of other layer 2 protocols which don't use MAC addresses -- so I'll mention one other important detail. --- Although the Ethernet protocol itself has been around for ~40 years now, for the majority of that time it mostly only existed "in the LAN". In fact, when it comes to "on the WAN", Ethernet is still a relative newcomer. Before ~15 years or so ago, pretty much no one was using Ethernet "on the WAN" -- instead, it was X.25 and frame relay and HDLC and PPP and ATM and POS on analog "leased lines" and ISDN and DS-{1,3}s and OC-{3,12,48,192}s. Along came MPLS, MetroE, EoMPLS, Carrier Ethernet, etc., and soon enough everyone was "tunneling" Ethernet between sites but we were still mostly using those "legacy" protocols "on the WAN". Over time, technology advanced to the point that "native" Ethernet eventually became feasible "on the WAN" -- in no small part because 1) Ethernet speeds kept increasing by an order of magnitude (!) every few years, 2) standardizing on Ethernet everywhere drove the costs down, and 3) Ethernet was "easy" (compared to all of those "WAN" protocols we were using up until this point) -- everybody already "knew" Ethernet because, by this time, everybody had been using it in their LANs for a decade or more! Although ATM and SONET (at least) are still around in (some parts of) some service provider networks, they are now the exception and Ethernet -- to butcher a phrase -- "has eaten the world" but, as I mentioned, Ethernet "on the WAN" is still a relatively new thing. --- So, I'll offer an alternative answer to your question: > Couldn't you simply put the next hop's MAC address (instead of IP address) into the routing table and be able to route packets just as well, with a lot less complexity? Sure, if you had done it about 30 years earlier!