The extended network instruction set includes several instructions related to network access: getipp, tpings, tpingr, divide, surf, ifsig, ttime.
Some of these instructions send messages from one Tierra node to another, based on the suggestion of an IP address in a register of the virtual CPU. Because the suggested IP addresses might not be valid, they are forced to match valid IP addresses from the IPMap array. The match is based on the closest Hamming distance (the minimum number of different bits).