Value,Next Payload Type,Reference
0,NONE,[RFC2408]
1,Security Association (SA),[RFC2408]
2,Proposal (P),[RFC2408]
3,Transform (T),[RFC2408]
4,Key Exchange (KE),[RFC2408]
5,Identification (ID),[RFC2408]
6,Certificate (CERT),[RFC2408]
7,Certificate Request (CR),[RFC2408]
8,Hash (HASH),[RFC2408]
9,Signature (SIG),[RFC2408]
10,Nonce (NONCE),[RFC2408]
11,Notification (N),[RFC2408]
12,Delete (D),[RFC2408]
13,Vendor ID (VID),[RFC2408]
14,"Reserved, not to be used",[Dukes]
15,SA KEK Payload (SAK),[RFC3547][RFC6407]
16,SA TEK Payload (SAT),[RFC3547][RFC6407]
17,Key Download (KD),[RFC3547]
18,Sequence Number (SEQ),[RFC3547]
19,Proof of Possession (POP),[RFC3547]
20,NAT Discovery (NAT-D),[RFC3947]
21,NAT Original Address (NAT-OA),[RFC3947]
22,Group Associated Policy (GAP),[RFC6407]
23-127,Unassigned,
128-255,Reserved for private use,