As shown is an IP packet header, which of the following statement is true?

A . The protocol number is 51, which means that the packet after the IP Header is the AH header
B . The packet must be an IPsec VPN packet installed only with AH
C . The protocol number 51, which means that the message after the IP Header is the ESP header
D . The message is a lpsec VPN message, and the data part of the message is encrypted

Answer: C