as an IXP-Operator I would like to comment this in three ways:

1. Requesting an Address-space be it v4 or v6 for an IXP-Infrastructure and not making it globally reachable somehow misses the point. It should be clearly reachable - ideally through *all* connected peers of the infrastructure. (they certainly can decide on the security for these destinations) ...

<http://psg.com/~randy/970210.nanog/sld008.htm> randy