Good points.
With current RIR rules, *no* ISP can give an absolute guarantee that it's prefix couldn't, at one point, be pulled off.
That is consistent with my understanding of the RIR policies. I think they go to some length to make it clear that the prefixes allocated to an ISP are not owned by the ISP and to their customers. For example section 4.1 of RIPE267
http://www.ripe.net/ripe/docs/ipv6policy.html
4.1. Address space not to be considered property
It is contrary to the goals of this document and is not in the interests of the Internet community as a whole for address space to be considered freehold property.
The policies in this document are based upon the understanding that globally unique IPv6 unicast address space is licensed for use rather than owned. Specifically, IP addresses will be allocated and assigned on a license basis, with licenses subject to renewal on a periodic basis. .....
So, it seems to me that creating implicit assumption that addresses allocated today from RIR's are "magical" and "will never be revoked", and "the ISP can give legal guarantees the prefix will never clash".
It seems to me that *practically*, recurring fees are a feature. If an ISP goes bankrupt, some other ISP actually has an incentive to obtain its business and the prefix -- in hope of getting a share of those recurring fees :-). Otherwise, the prefix could just rot and be returned to RIR (for example).
In this case there is also the problem that if the contact information for the allocation is lost or out of date, then it will be difficult for whoever obtains the assets of the bankrupt ISP to determine if the allocation is still in use. Consequently there is a reasonable likelihood that it will be reassigned to someone else and made routable.
The more I think about it the less I like the idea that prefixes from the globally routable address space will be used for local addressing. I understand there isn't anything that can stop this from happening occasionally, but I strongly doubt that it would ever become official RIR policy.
Bob
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