The existence of a forward mapping is not a necessary technical
precondition for you to insert a reverse mapping which points in
the right direction, i.e. at the organization operating the
boxes. However I also have trouble seeing why any ISP would
willingly decline to register it's boxes in the DNS.
Welcome to the USA, Land of a thousand startup ISP's.
They decline for a couple of reasons:
- They don't have DNS running internally
- They perceive the EP node to be "outside" their domain
- They don't know/care
- A default is provided.
Now I will agree that the forward mapping is not a necessary
technical precondition, there is a need to the reverse mapping.
That mapping needs a name.