This draft from the IETF based upon work from Cisco, Juniper, and Google is titled
Enterprise Multihoming using Provider-Assigned Addresses without Network Prefix Translation: Requirements and Solution.
Quoting from the lead in section:
Connecting an enterprise site to multiple ISPs using provider-
assigned addresses is difficult without the use of some form of
Network Address Translation (NAT). Much has been written on this
topic over the last 10 to 15 years, but it still remains a problem
without a clearly defined or widely implemented solution. Any
multihoming solution without NAT requires hosts at the site to have
addresses from each ISP and to select the egress ISP by selecting a
source address for outgoing packets. It also requires routers at the
site to take into account those source addresses when forwarding
packets out towards the ISPs.
This document attempts to define a complete solution to this problem.
It covers the behavior of routers to forward traffic taking into
account source address, and it covers the behavior of host to select
appropriate source addresses. It also covers any possible role that
routers might play in providing information to hosts to help them
select appropriate source addresses. In the process of exploring
potential solutions, this documents also makes explicit requirements
for how the solution would be expected to behave from the perspective
of an enterprise site network administrator.
Some interesting quotes:
"It is not reasonable to expect an
enterprise network operator to change the routing topology of the
site in order to deploy IPv6."
"Mechanisms have been proposed to allow hosts to
choose the source address for packets in a fine grained manner. We
will discuss these proposals in Section 4. However, interacting with
host operating systems in some manner to ensure a particular source
address is chosen for a particular destination prefix is not what an
enterprise network administrator would expect to have to do to
implement this routing policy."
"With IPv4, this problem is commonly solved by using [RFC1918] private
address space within the multi-homed site and Network Address
Translation (NAT) or Network Address/Port Translation (NAPT) on the
uplinks to the ISPs. However, one of the goals of IPv6 is to
eliminate the need for and the use of NAT or NAPT. Therefore,
requiring the use of NAT or NAPT for an enterprise site to multihome
with provider-assigned addresses is not an attractive solution."