3.1.1. Background
3.1.1. Background
There were a range of choices available when choosing the size of the prefix and Global ID field length. There is a direct tradeoff between having a Global ID field large enough to support foreseeable future growth and not using too much of the IPv6 address space needlessly. A reasonable way of evaluating a specific field length is to compare it to a projected 2050 world population of 9.3 billion [POPUL] and the number of resulting /48 prefixes per person. A range of prefix choices is shown in the following table:
| Prefix | Global ID Length | Number of /48 Prefixes | Prefixes per Person | % of IPv6 Address Space |
|---|---|---|---|---|
| /11 | 37 | 137,438,953,472 | 15 | 0.049% |
| /10 | 38 | 274,877,906,944 | 30 | 0.098% |
| /9 | 39 | 549,755,813,888 | 59 | 0.195% |
| /8 | 40 | 1,099,511,627,776 | 118 | 0.391% |
| /7 | 41 | 2,199,023,255,552 | 236 | 0.781% |
| /6 | 42 | 4,398,046,511,104 | 473 | 1.563% |
A very high utilization ratio of these allocations can be assumed because the Global ID field does not require internal structure, and there is no reason to be able to aggregate the prefixes.
The authors believe that a /7 prefix resulting in a 41-bit Global ID space (including the L bit) is a good choice. It provides for a large number of assignments (i.e., 2.2 trillion) and at the same time uses less than .8% of the total IPv6 address space. It is unlikely that this space will be exhausted. If more than this were to be needed, then additional IPv6 address space could be allocated for this purpose.