In 11.2 Pmon process propagates the service metrics to the listeners registered in local_listener and remote_listener initialization parameter.
As the remote_listener specifies specifies the address of scan listener and the local_listener parameter specifies the address of the VIP listener, PMON process propogates the service metrics to both SCAN and VIP listeners.
You can trace listener registration using the following command.
alter system set event=’immediate trace name listener_registration level 15′;
Now in 12c version listener registration is permed by a new mandatory background process named LREG.
And if you want to trace then LREG trace file getting to all info about listener registration.
Advantage : Not recommneding that you create 50+ of unnecessary services,you should create
as many services as you need to split the application into manageable and disjointed workload.
In 11gR2 if there are 50+/100+ services and listeners then there is a possiblilyt that the PMON process
might spend more time on service registration to listener.
But in 12c this possibility is eliminated as the LREG backgroud process which is totally dedicated for registering the services to Listener.
and PMON is freed from listener registration.