> You mean aside from applications understaning that an ICMP Destination > Unreachable / Administratively Prohibited response from the site firewall? > > For that matter, IPv6 machines arguably could try their Site Local address > and be given that same feedback from the border router or firewall how does any party - the host, border router or firewall - know whether the SL address is from that site or some other site? SLs are inherently ambiguous. > , and use > the response as an indication to go use their assigned global address. if the destination has a global address, it should *always* be used in preference to the site local, at least in the absence of external configuration. > We have the problem of scoped addresses whether the "site local" mechanism > is retained or not. I disagree, or at least, I think it's misleading to use the term "scoped addresses" to cover all filtering, because this is conflating two things - use of filtering on one hand and use of ambiguous addresses on the other. It's useful to be able to refer to a host even if you can't send traffic there. Keith