[Mobike] Changing to port 4500

[Eric Fung]

Tero Kivinen wrote:

> The RFC 4555 has a bit underspecified text saying we change if both
> ends supports both, but actually we do not need to  know whether
> remote end supports MOBIKE, knowing that it supports NAT-T is
> enough. Anyways examples make it very clear that we change to port
> 4500 for the IKE_AUTH.

If there is no NAT between the peers and we change to port 4500, should ESP 
packets be UDP encapsulated or not?  I don't see any pertinent guidance in RFC 
4306 and at least one implementation I'm testing against differs in its 
interpretation.

Thanks.