(Sorry for the previous incomplete message)
I have a comment on the "last resort" rule, that say, everything being equal,
perform longest prefix match an all bits from 1 to 128.
I would like to suggest to limit the match to the first 64 bits.
The danger of doing match on all the bits is to have unpredictable behavior
and difficult to diagnose problem.
Let say that you have to hosts A & B on the same IPv6 subnet, and both host
have another direct connection (e.g. serial link or another ethernet link
at a lower speed) for back-up
Let say that all addresses have global scope. All things being equal,
A and B will resort to longest prefix match. Both prefix being /64,
the algorithm will try to match the other bits. and then... the choice of
the selected link is unpredictable. So depending on the brand and
date of make of the ethernet NIC, communication between A and B
will either take the normal link or the backup link.
My take is that this unpredictability will lead to very difficult to
diagnose problem.
I would like to suggest to restrict longest prefix match to /64
and,if all things are still equal, apply a predictable algorithm to
choose which address to select. example: always take the prefix
with the highest value. Or best, apply local knowledge when available,
like route metric, interface bandwidth,...
Then, all machines on the same subnet will behave the same way and
network administrator will have less trouble with this.
- Alain.
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