3.7.5.1 Receiving Message #1
On receipt of message #1, the host MUST check for the presence of the "MS-Negotiation Discovery Capable" vendor ID payload (as specified in section 3.7.4.1). If the "MS-Negotiation Discovery Capable" vendor ID payload is present in the message, the host MUST set the Negotiation Discovery Supported flag for the corresponding MMSAD entry.
Then, the host MUST construct message #2, as specified in [RFC2409] section 5, and add the "MS-Negotiation Discovery Capable" vendor ID payload to advertise its negotiation discovery capability.