Often, participants expect to have an IP address assigned for their
use on an exchange. Usually these delegations are from a common
block. Where they are not, its hard to tell an exchange from a
bunch of point2point links. LINX and PAIX have IPv6 prefixes that
participants can use.
or, use link-local address on IX switch as documented in
draft-kato-bgp-ipv6-link-local-01.txt.
itojun