4shared

In order to ensure proper working of carrier-grade NAT (CGN), and, by doing so, alleviating the demand for the last remaining IPv4 addresses, a /10 size IPv4 address block was assigned by Internet Assigned Numbers Authority (IANA) to be used as shared address space.This block of addresses is specifically meant to be used by Internet service providers (or ISPs) that implement carrier-grade NAT, to connect their customer-premises equipment (CPE) to their core routers.
Instead of using unique addresses from the rapidly depleting pool of available globally unique IPv4 addresses, ISPs use addresses in 100.64.0.0/10 for this purpose. Because the network between CPEs and the ISP's routers is private to each ISP, all ISPs may share this block of addresses.

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