Thus spake "Rémi Denis-Courmont" <[EMAIL PROTECTED]>
This assumes that one may use an ULA (IPv6) to reach a globally
routable (IPv6) address. In other words, that someone has introduced
some kind of NAT or transparent proxy in the middle.
That's not the only case, and hopefully one that will never happen.
A site may number their hosts with both global addresses and ULAs. Hosts
intended to communicate with the internet would have both, whereas
"internal" hosts like servers may have just ULAs.
I believe the intent when we developed ULAs was:
1. when contacting a global address, the preferred source is a global
address
2. when contacting a ULA, the preferred source is a ULA from the same prefix
There was a bit of debate about the correct source address when contacting a
ULA from a different prefix than the one used locally. I don't think this
was ever resolved.
For an explanation of this case, consider two companies that have a private
interconnection. If both have ULAs and globals assigned to hosts, should
they communicate using the globals or the ULAs? If only one has globals
assigned, should the other site contact it using its globals or ULAs as the
source address?
The rules on this were pretty clear for SLAs since one couldn't use them for
inter-site communication even if one wanted to; however, ULAs can be used in
this role similarly to globals depending on how routing and ACLs are set up.
In some cases, they may even have greater reachability than globals...
S
Stephen Sprunk "Stupid people surround themselves with smart
CCIE #3723 people. Smart people surround themselves with
K5SSS smart people who disagree with them." --Aaron Sorkin
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