In article , Andrew
Sarangan wrote:

The Dayton Class C airspace sits right next to the Wright-Patterson AFB
Class D airspace. A vector for the ILS approach often takes us over or
through the class D airspace. If we are VFR, I always verify with the
approach controller if we are ok to enter the class D. I have received
mixed answers to this query. Sometimes the controller will thank me for
asking and confirm that the class D controller is aware of us. Sometimes he
will change the vector upon my query. Sometimes the controller has told me
that I am ok to enter the class D airspace as long as I am talking to him.
One controller was even annoyed that I asked him, and proceed to say that I
was ok to transition the class D. What is the normal procedure in
situations like this?

As Paul said, there is a Letter of Agreement.
The Columbus OH airspace has three CDAS beneath the KCMH CCAS.
There is a LOA between Columbus and each of the three satellites that
reduces the CDAS from 4000 AGL to 2500 AGL, giving the CCAS Approach
control the airspace 2500 and above.
(Note that 2500 AGL is the floor of the CCAS surrounding Columbus.)