126.96.36.199.4 Using Negotiated Flags
The client and the server often need to know the capabilities of their partners in their client/server communications. For example, it is sometimes necessary or desirable for a newer version client to avoid calling a method that the older version server does not implement. Similarly, the new server would avoid sending fields that the older client is going to treat as dummies and ignore. To make this possible, the client and the server need to establish a common set of capabilities that both the client and the server support.
For this reason, the NetrServerAuthenticate3 method (section 188.8.131.52.2), which is called early on during setup of the secure channel between the client and the server, includes the NegotiateFlags parameter. The NegotiateFlags parameter uses a set of bit flags to carry the client and server capabilities. The client sets its capabilities on input, and the server responds with capabilities that it supports out of those sent by the client. The resulting set of bit flags is the set of capabilities that the client and the server mutually support.