3.3.5.14 Receiving a Attach Command

If the connection (1) is not in the ‘established’ state, or a session with the session identifier in the EventId field already exists, or the AttachSessionId state variable (as specified in section 3.3.1) for this connection (1) already exists, the recipient MUST close the connection (1) as specified in section 3.1.4.2 with a ReasonId of TooManyUnknownSessionCmds (0x0f). Otherwise, if the recipient does not close the connection (1) with a ReasonId of TooManyUnknownSessionCmds (0x0f), the value of the EventId field MUST be added to the AttachSessionIds.

The recipient MUST extract the contained AuthenticationToken field, and submit it to SSTP Security protocol validation as specified in [MS-GRVSSTPS]. The recipient MUST respond to the client with the command and message contents as determined by [MS-GRVSSTPS], to be sent on the attach session.