Mastering pfSense - Second Edition

NAT essentials

NAT was a standard developed to deal with the depletion of IPv4 addresses. Since IPv4 addresses are 32-bit addresses, there are potentially 4.3 billion addresses available. But since IPv4 was initially divided into Class A networks (first octet = 1 to 126, 8-bit subnet, over 16 million nodes per network), Class B networks (first octet = 128 to 191, 16-bit subnet, 64K nodes per network) and Class C networks (first octet = 192 to 223, 24-bit subnet, 254 nodes per network), the situation was even worse. Class A and Class B networks were too large to be used efficiently even by large organizations, and many Class A networks were assigned to large corporations, thus further reducing the pool of available addresses. The next smallest ...