NAT

Network Address Translation (NAT) was developed specifically to counter the lone weakness inherent in the private addresses of RFC 1918. That's not to suggest that it makes those nonunique addresses globally routable, because it doesn't. Rather, it lets you translate those nonunique addresses to unique and routable addresses at the edge of your network. This permits access to and from the global Internet. In other words, you operate with two sets of addresses: You would have your private RFC 1918 addresses configured on endpoints throughout your network, and then a globally routable block of addresses would be configured on your NAT device. NAT would be responsible for correlating the internal and global addresses and translating as needed ...

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