Detailed Questions About RPC Protocol

We are experimenting with an RPC application proxy between member servers
and our AD domain controllers. We set up the proxy to support only two
UUIDs: NETLOGON and NTDS. Logins to the domain are working fine. But
when we run Microsoft's RPCDUMP from the client to the server to actively
examine which RPC services show as available, we get an immediate failure
and RPCDUMP returns no services. Questions are:

1) At a detailed protocol level, does the RPC protocol require that a
requestor get a list of all available RPC services before requesting a
specific service? Or can an RPC client simply make an immediate request
for a specific service and get a response pointing to the service (UUID)
port?

2) Which UUID(s) are responsible for supplying a client with a list of all
available RPC services?

3) Given the application described above, which UUIDs at minimum will a
member server need to be able to function properly against the AD domain
controller(s) in the forest?

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Will