When we think of internet, it seems amazing to see that there are so many computers connected. This was made possible by the internet protocol version 4 provides 232 (4,294,967,296) addresses even though not all of them are usable. There are mostly saturated and the total number becomes about 4.2 billion and that is about all accounted for now. The new version of internet protocol is called version 6 which provides upto 2128 addresses which computes to 3.4 x1038 individual computers. So theoretically, sitting on one computer you could reach any of the other devices that are attached to it. That makes for an interesting network.
Now compare that with the cells in the human body. It is estimated that there are about 50 trillion, i.e. 5 x 1013 cells in a human body. Multiply that with the total world population of say 10 billion (actual number is ~7 billion as of today) and you get a number:
5 x 1013 * 1 x 109 = 5 x 1022 and this number is still smaller than the number that is possible with the new internet protocol.
This means that it is possible to label every cell of every person with a unique number and not run out of numbers.
But also leads to another thought exercise: It would be great to be able to address each and every cell of the human body and control it, especially the immune cells to be able to control allergies or auto-immune reactions. If you had to design such a system to control say 4 billion cells then all you need is 32 different of ON-OFF switches 232 and you could make each cell individually addressable. This is not such a difficult problem. It is currently possible to measure the levels of 32 different antigens on the cell surface and so it should be possible to have unique cell addressing capability.
What this will enable is to control exactly the cell that we want and then be able to control its activity. It will need some design but is possible with our current technology.