RE: Issue: When to do return-routability tests (#6)

Jari Arkko wrote: 
>
> This is a related issue, but partly different too. I agree that
> empty informational exchanges are not sufficient for an RR
> test, and a nonce is needed. Basically, an empty informational
> exchange just proves that the answer came from the peer, but
> not that it came from the address we wanted to test. I guess
> you could amend my list above as follows;
> 
>   - None, no tests.
> 
>   - A party willing to answer is on the path to the claimed
>     address. This is the basic form of return routability
>     test.
> 
>   - There is an answer from the tested address, and that
>     answer was authenticated (including the address) to be
>     from our peer.
> 
>   - There was an authenticated answer from the peer, but
>     it is not guaranteed to be from the tested address
>     or path to it (because the peer can construct a
>     response without seeing the request).
> 
> The last option corresponds to making an empty informational
> exchange. I think the first and the last options are not
> practical options; its either the second or the third
> option that we should adopt.

I my opinion, "Return routability" usually means the second one:
we verify that we have a route back to the party who made the 
request. This is also what normal IKEv2 provides (either
statelessly using COOKIE payload, or with state and Ni/Nr).

Best regards,
Pasi