3.3.4.1 Start of an IKE MM SA Negotiation
As part of the construction of message #1 for a new MM SA negotiation (as specified in [RFC2409] section 5), an IKE fragmentation-supporting host MUST include a "FRAGMENTATION" vendor ID payload (that is, a vendor ID payload that is generated by using the Vendor ID string "FRAGMENTATION", as specified in [RFC2408] section 3.16) to advertise its fragmentation capability.