From Section 1 of RFC 4191:
We use Router Advertisement messages, instead of some other
protocol like
RIP [RFC2080], because Router Advertisements are an existing
standard,
stable protocol for router-to-host communication. Piggybacking this
information on existing message traffic from routers to hosts reduces
network overhead. Neighbor Discovery shares with Multicast Listener
Discovery the property that they both define host-to-router
interactions,
while shielding the host from having to participate in more general
router-to-router interactions. In addition, RIP is unsuitable
because it
does not carry route lifetimes so it requires frequent message
traffic with
greater processing overheads.
indeed. MSR is a router-to-host mechanism. the CPE acts for some
purposes as a host on the upstream interface. do you expect the MSR
routes to be limited to be used only for the host part of the CPE (i.e
communication originating from the CPE) or to make it into the CPE's
forwarding table?