The Negotiation Send/Reply Option is shown in Figure 6. The value of the Kind is 20 in the Negotiation Send Option and 21 in the Negotiation Reply Option. These options can send a list of security type. A maximum number of the security service type that the option can contain is 38, because the length of the TCP option is limited in 40 octets.
The format of security type data is shown in Figure 7. The security type data is 1 octet long. The L/G field(1bit) determines whether local or global security type is set up. The Type field (7bit) identifies whether type of security service uses.
Figure 6: Negotiation Send/Reply Option
Figure 7: Security Service Type Format