IPv4 address exhaustion
IPv4 address exhaustion is the depletion of the roughly 4.3 billion addresses IPv4's 32-bit address space provides, a limit the internet's growth reached faster than IPv6 -- which uses a 128-bit address space large enough that exhaustion isn't a practical concern -- was deployed to replace it. IANA allocated its last remaining IPv4 address blocks to the regional internet registries in 2011, and several registries have since run out of their own free pools too. Rather than switching networks to IPv6-only, most ISPs responded with mitigations that stretch the existing IPv4 supply: Carrier-Grade NAT (CGNAT) shares one public address across many customers, using the shared address block RFC 6598 reserves for exactly that purpose. AdminKit's CGNAT guide covers why that specific mitigation, adopted because of this exhaustion, causes shared blacklist status and broken port forwarding for affected customers.
By AdminKit team, Netbase JSC · Updated