Bob Hinden wrote:
ID/locator split, which I've been
a proponent of for very many years, works a lot better with more bits,
because it allows topological addressing both within and outside an
organization.
To confirm what your are saying about an ID/locator split in
IPv6, that the other reason why we went with 128-bit address
with a 64/64 split as the common case and defining IIDs
that indicate if they have global uniqueness. This creates
a framework that an ID/locator split could be implemented.
I actually implemented such a system about 10 years ago
and it worked fine.
It was an experiment for hosts to use multiple IPv4 and IPv6
addresses, some of which may have ID/loc separation. DNS
was used for ID->loc mapping. Mobility was also supported
with multiple home locators and multiple foreign locators.
We did something related to end to end multihoming and
happy eyeball.
ID locator separation was good, because it requires about
half amount of space to store multiple addresses sharing
an ID.
Moreover, rewriting destination locators enables elegant
forwarding from home agents to mobile nodes without
tunneling (and associated MTU tax), if transport check
sums do not involve locators.
But, that's all. It was not very interesting that I
abandoned further work on it after government funding
period expired.
Opinions vary if ID/locator split is useful, but we have a
framework that would allow it without having to roll
out another version of IP. A win IMHO.
Assuming address must be 16B long, it may be good to
have ID/loc separation.
However, if we have choice, having 8B long addresses
is much better, because it is more compact than 16B
address with ID/loc separation.
Even with 8B addresses, we can rewrite destination addresses,
if there is a destination header option (or a mandatory field)
"original destination address" to be used to confirm transport
identity and checksum.
So, along with the failure with a lot of confusion to have
SLAAC, we can conclude that IPv6 addresses should have been
8B long.
Maybe, even with the current IPv6 packet format, routers
can look only at first 8B of addresses and ignore the
latter 8B (used as "original source/destination address"
for source/destination address rewriting).
Masataka Ohta
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