james woodyatt wrote:

> The latest message I received concluded with these paragraphs:
>>
>> In summary, I agree that your proposal will work, if both B2B partners
>> agree to advertise their FC00:: routes to each other via the private
>> link.  But there is some risk to the business from the additional
>> routes in the route table.  Also some extra complexity from the
>> additional static configuration (enabling use of the fc00:: subnet on
>> the host, and possibly the fc00::/7 -> route if that can't be put in a
>> router advertisement).

Just curious - assuming that ULAs should be used at all (and it's not
immediately clear that they should), why wouldn't an RA containing the
ULA prefix suffice to enable use of the subnet on each host?

To me it seems like more problems are likely to result from use of ULAs
as secondary prefixes, than from use of PA or PI global addresses.  In
particular, applications have to know whether to use a ULA or P* address
as a source and/or destination address, and default address selection
rules don't always do the right thing.  So you might have to statically
configure each app (because the "right thing" will vary from one app to
the next) but not each host.

>> I don't consider the operational impacts to achieve "no IPv6 NAT
>> purity" worth it.  IPv6 to IPv6 NAT is an important tool in the
>> network engineer's toolbox.

Reading this, it's difficult to not be reminded of Maslow's hammer that
makes everything look like a nail.

Still, it's important to understand this case better.  Either we need to
address it in an update to RFC 4864, or we need to make sure that IPv6
NAT satisfies this case.  (or maybe both, on the assumption that there's
too much mindshare behind NAT to expect network engineers to give it up
as a condition of IPv6 transition.... but we can hope that they'll learn
eventually to do without it.)

Keith
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