5 ms·

MAC addresses are link-local, not global. Your device and my device could have the same MAC address and everything works fine until we find ourselves on the sa

MAC addresses are link-local, not global. Your device and my device could have the same MAC address and everything works fine until we find ourselves on the same L2 network. And there's practical limits to how large a single L2 network can be, and it's way smaller than 48 bits of space.

throw0101a 5y ago
Yes, I know. But I think you misunderstood this sub-thread. IPv4 has 32-bit addresses, and we've run out of those, which necessitated a new protocol (IPv6) with a larger addresses space (and the use of NAT until it's rolled out everywhere). However, the GP said: > Sometimes I imagine an "alternate history" where IPv4 had 64-bit addresses […] Which would have allowed for continued use of this alternate-history-IPv4 without having to NAT and without all the work to enable IPv6. My observation was that 64b addresses would probably not not even been needed, as we're using "only" 48b for Ethernet MAC addresses and we haven't run out of those yet, so an alternative-history-IPv4 with "only" 48b addresses (instead of 64b or IPv6's 128b) would probably also been enough. At least until now, early 2022. I'm sure at some point the alternate-history-IPv4 addresses would have run out, and an alternate-history-IPv5/6 would have had to have been developed eventually too. > And there's practical limits to how large a single L2 network can be, and it's way smaller than 48 bits of space. Well IPv6 subnets are /64, so ¯\_(ツ)_/¯. (Though 2^64 hosts are not actually expected to live in a single subnet: that's the equivalent of four billion Internets.)
- NavinF 5y ago
  > an alternative-history-IPv4 with "only" 48b addresses (instead of 64b or IPv6's 128b) would probably also been enough MAC address can be assigned in arbitrarily small blocks whereas IP addresses must be assigned as large prefixes, ideally one prefix per org. Otherwise the internet routing table would be too large. I don’t think 2^48 is reasonable right now without NAT and it certainly won’t be enough in the near future. Also 48b MAC addresses are kinda small. InfiniBand uses 64b and newer protocols should do the same.
  - throw0101a 5y ago
    > MAC address can be assigned in arbitrarily small blocks Not really. Of the 48b available, the first 24 are assigned to an organization: * https://en.wikipedia.org/wiki/Organizationally_unique_identifier https://en.wikipedia.org/wiki/Organizationally_unique_identi... * http://standards-oui.ieee.org/oui/oui.txt http://standards-oui.ieee.org/oui/oui.txt then they can assigned the other 24b as they wish. This is in some way similar to an IP prefix being assigned, which can then be used however the assignee wishes. 48b would have lasted longer than 32, perhaps delaying the need for NAT (RFC 1631 from 1994), but certainly at some point an address extension would have been needed. Of course in the 1970s it would have been hard/impossible to predict needing more than four billion addresses for a research/academic network.
    - NavinF 5y ago
      You don’t need an OUI. They sell smaller blocks: https://standards.ieee.org/products-services/regauth/oui36/ https://standards.ieee.org/products-services/regauth/oui36/

throw0101a 5y ago

Yes, I know. But I think you misunderstood this sub-thread. IPv4 has 32-bit addresses, and we've run out of those, which necessitated a new protocol (IPv6) with a larger addresses space (and the use of NAT until it's rolled out everywhere). However, the GP said: > Sometimes I imagine an "alternate history" where IPv4 had 64-bit addresses […] Which would have allowed for continued use of this alternate-history-IPv4 without having to NAT and without all the work to enable IPv6. My observation was that 64b addresses would probably not not even been needed, as we're using "only" 48b for Ethernet MAC addresses and we haven't run out of those yet, so an alternative-history-IPv4 with "only" 48b addresses (instead of 64b or IPv6's 128b) would probably also been enough. At least until now, early 2022. I'm sure at some point the alternate-history-IPv4 addresses would have run out, and an alternate-history-IPv5/6 would have had to have been developed eventually too. > And there's practical limits to how large a single L2 network can be, and it's way smaller than 48 bits of space. Well IPv6 subnets are /64, so ¯\_(ツ)_/¯. (Though 2^64 hosts are not actually expected to live in a single subnet: that's the equivalent of four billion Internets.)

NavinF 5y ago
> an alternative-history-IPv4 with "only" 48b addresses (instead of 64b or IPv6's 128b) would probably also been enough MAC address can be assigned in arbitrarily small blocks whereas IP addresses must be assigned as large prefixes, ideally one prefix per org. Otherwise the internet routing table would be too large. I don’t think 2^48 is reasonable right now without NAT and it certainly won’t be enough in the near future. Also 48b MAC addresses are kinda small. InfiniBand uses 64b and newer protocols should do the same.
- throw0101a 5y ago
  > MAC address can be assigned in arbitrarily small blocks Not really. Of the 48b available, the first 24 are assigned to an organization: * https://en.wikipedia.org/wiki/Organizationally_unique_identifier https://en.wikipedia.org/wiki/Organizationally_unique_identi... * http://standards-oui.ieee.org/oui/oui.txt http://standards-oui.ieee.org/oui/oui.txt then they can assigned the other 24b as they wish. This is in some way similar to an IP prefix being assigned, which can then be used however the assignee wishes. 48b would have lasted longer than 32, perhaps delaying the need for NAT (RFC 1631 from 1994), but certainly at some point an address extension would have been needed. Of course in the 1970s it would have been hard/impossible to predict needing more than four billion addresses for a research/academic network.
  - NavinF 5y ago
    You don’t need an OUI. They sell smaller blocks: https://standards.ieee.org/products-services/regauth/oui36/ https://standards.ieee.org/products-services/regauth/oui36/