issue 12: interaction with other protocols doing RR

Background: a number of protocols employ return
routability tests. In the mobility space we have
this at least in MOBIKE, Mobile IPv6, MULTI6, and
HIP.

Tero's design document discusses some differences
these tests have in different contexts; not all
do exactly the same thing even if all at least
verify there's someone willing to respond on the
path towards the tested address.

I would like to suggest that we do our own specific
type of test, but allow same tests to be "reused" across
protocols where this makes sense. That is, in MOBIKE
we do our own test that verifies liveness of the address
and that the peer is indeed still the same IKEv2
node and has knowledge of some secret keying material.
In addition, we add a note saying that the use of
the results of this test may be possible in other
protocol layers*.

Ok for everyone?

--Jari

*) The example that comes to my mind is that since the
mobile node - home agent interface in mobile IPv6 runs
with IPsec, then the use of MOBIKE in that context
would provide an RR test to home registrations. That
does not exist in Mobile IPv6 at the moment, but if
it were included then Mobile IPv6 home agent service
could easier be offered to "unknown" peers. Currently
"unknown" peers are only support as correspondent
nodes.