William Herrin wrote:
Certainly we would appreciate other opinions about what the right length of a change-over time would be, especially from the operational communities that will be most impacted by this change.
Considering the possibility that, in a long run, remaining 12 sets (4 and 6) of IP addresses will also change, the proper length should be determined assuming all the 13 sets of addresses will change (not necessarily at the same time).
A server generation is about 3 years before it's obsolete and is generally replaced. I suggest making the old address operable for two generations (6 years) and black-holed for another generation (3 more years).
You are assuming managed servers under Moore's law. But, after Moore, a server generation will be longer. Moreover, a linux-based black box, vendor of which has disappeared, may be used for 10 or 20 years without being managed. Then, another important period is the period to reserve the IP addresses once used for root servers. If the addresses are reused by some bad guys, systems depending on them can easily be compromised. For the reservation period, 50 years of reservation period of ISO3166 country codes seems to be reasonable. And, if the addresses are reserved, there is no reason not to keep using the addresses as alternative addresses of active root name servers. Masataka Ohta PS First of all, it is a bad idea to change the addresses of root servers. For political ceremony, it is enough to transfer address blocks to LACNIC.