• 32-bit address space vs 128-bit address space
• Written representation (dotted-decimal vs. colon-separated-hex)
• Variable host address space vs. fixed host address space
• Subnet only subdivides the network prefix space
• Non-standard vs. standardized anycast
• NAT layer (Carrier or residential) vs scoped addresses
• First specified: RFC 760 (in 1980) vs RFC 1883 (in 1995)