Common Misconception With Spread Spectrum IP Addressing the 32-bit Source Address Field is Shifted LEFT 2-bits by the originator of the packet. That Folds the IPv4 Legacy Address Space into 1/4th tsize table The lost 2-bits are stored in the Right-Most 2 bits of the 32-bit field and in other places in the IPv4 Header The Destination can easily recover the Source Address - if the proper algorithms are in use Responses blindly sent back to the shifted Source Address may fall into agile hands or not With the advanced Spread-Spectrum techniques, additional addressing bits are created from the noise intentionally stored in the Right-Most 2 bits NANOG Operators buying /8s or /6s may want to look at the Spread-Spectrum CODE in the Linux-based CPE Routers The following table is deprecated and 1/4th the size: http://www.iana.org/assignments/ipv4-address-space/ipv4-address-space.txt With Spread-Spectrum collisions and mis-directions are OK and expected but other techniques ensure the packets get to the right place. http://NANOG.GURU