Julian, I think the one problem we need to avoid is
What do you do when two occurrences of FEC0::0001/64 exist
within a single routing domain?
This is the problem created by the current SL definition when
two 'sites' are united by merger or VPN and they both happen
to have a subnet #1.
We shot ourselves in the foot by creating this problem in the
initial IPv6 addressing architecture.
Brian
"Sellers, Julian P" wrote:
>
> Keith's multi-party applications won't work if the parties refer non-global
> addresses to each other. Margaret recommends that everyone use global
> addresses, but filter certain prefixes at various administrative boundaries.
> How, then, do Keith's applications know which addresses have global scope
> and which do not?
>
> A tacit assumption seems to be that applications will not have to deal with
> link-local addresses. I'm aware of the recommendation not to place
> link-local addresses in the DNS, but I know of no prohibition of
> applications communicating via link-local addresses. If they may do so, is
> this less problematic than using site-local addresses?
>
> Since I know nothing about filtering in routers, can someone tell me why
> filtering on FEC0::/10 is more complex than filtering on prefixes chosen by
> the local administrator(s)? And concerning Margaret's point on nesting
> sites, could routers not filter within FEC0:0:subn:etid::/64 addresses?
>
> Again citing the disclaimer re my lack of knowledge, the
> filtering-on-locally-designated-prefixes method seems unwieldy compared to
> the filtering-on-well-known-scope method. Implementations can allow an
> administrator to configure address scope preferences using the well-known
> scopes. Nodes (applications) on the same subnet could then have addresses
> of different scopes. This would be cumbersome at best without well-known
> scopes.
>
> Some have complained about the complexity of always disambiguating
> site-local addresses by means of their zone identifiers. This seems
> insignificant to me; the same must be done for link-local addresses. The
> zone identifier accompanies the address wherever it goes. Right?
>
> I understand that sites that merge would have to renumber if their subnet
> IDs conflicted. Some have stated that a disconnected site using site-local
> addresses must renumber when it connects to the Internet. Wouldn't the site
> simply add the new prefix(es), and the nodes use the new addresses and/or
> site-local addresses based on local configuration? Connections using
> site-local addresses would not be affected by connection to the Internet.
>
> Since so many wise people object to site-local addressing, the problems must
> be greater than they appear from behind these cube walls. But I have not
> seen answers to these questions (or maybe I failed to comprehend). I look
> forward to having my horizons expanded.
>
> Julian Sellers
> Enterprise Server Communications Engineering
> Unisys Corporation
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