Explanation/Reference:
Explanation:
The remaining four parts of the ESP are all encrypted during transmission across the network. Those parts are as follows:
The Payload Data is the actual data that is carried by the packet.

The Padding, from 0 to 255 bytes of data, allows certain types of encryption algorithms to require the

data to be a multiple of a certain number of bytes. The padding also ensures that the text of a message terminates ona four-byte boundary (an architectural requirement within IP).
The Pad Length field specifies how much of the payload is padding rather than data.

The Next Header field, like a standard IP Next Header field, identifies the type of data carried and the

protocol.
Reference: http://www.cisco.com/c/en/us/td/docs/net_mgmt/vpn_solutions_center/2-0/ip_security/ provisioning/guide/IPsecPG1.html