The sad part to me is that the original IP header included variable-length addresses up to 128 bits, using two 4-bit fields called Source Address Length (SAL),

The sad part to me is that the original IP header included variable-length addresses up to 128 bits, using two 4-bit fields called Source Address Length (SAL), and Destination Address Length (DAL). [1] Early hardware implementations could have settled on 32-bit, but 48-bit would make more sense to be in line with EUI-48/MAC-48 (ethernet frame). The world could then gradually upgrade hardware over the decade to handle a larger address. [1] https://www.rfc-editor.org/ien/ien28.pdf https://www.rfc-editor.org/ien/ien28.pdf