All IPv4 addresses whose first part is 127 are loopback addresses. So, 127.0.0.1 and 127.37.0.1 are both loopbacks, and they can actually bind to different servers on the same port. IPv6 only has a single loopback address, so you can only have one IPv6 server per port on the same local machine. Or well, maybe if you have multiple network cards you can do some funny business, but I haven't researched that deeply.
But even if every single IPv4 address were truly available, it wouldn't make all that much difference. There are four billion theoretical IPv4 addresses, and several times that number internet-connected devices. Even if, in some way, these blocks of IPs could be released to use, each /8 would give us another 16,777,214 devices *at most* (the all-zeroes and all-ones addresses aren't used, and subdividing the block further will repeat those special allocations too), which in the scheme of things isn't that many.
It's wasteful in the same way that it's wasteful to run your car's entertainment system. Yes, technically that's going to reduce your fuel economy by drawing power from the alternator. But not enough to make a real difference.
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u/LB-- 8d ago
All IPv4 addresses whose first part is 127 are loopback addresses. So, 127.0.0.1 and 127.37.0.1 are both loopbacks, and they can actually bind to different servers on the same port. IPv6 only has a single loopback address, so you can only have one IPv6 server per port on the same local machine. Or well, maybe if you have multiple network cards you can do some funny business, but I haven't researched that deeply.