10 years is the ICANN limit but Network Solutions offers 100 years. According to the fine print what they do is actually register it for 10 years and then every year for the next 90 years they register it for an additional year.

They are betting that they will earn more than enough from investing your up front 100 year payment to more than cover future increases in the cost of those one year extensions.

Their customers are betting that Network Solutions or some successor will be around long enough and that domain names will work like the do now long enough that this will be worth it.

Most registries limit domain lifetimes to 10 years. You can't renew a domain if doing so would put the lifetime beyond 10 years -- the registry will refuse to perform the operation.

Clearly there are companies that offer extension as a service, you pay 20 times as much and they promise to extend your domain 10 times.

That just moves the problem though, how likely is it that that company will be around in 90 years to perform the last extension?

That may vary by registrar. My .com domain is about 2 years out from renewal and the most it will let me add is 8.