Which of the following fields make up the header of an ESP packet? (Select 2 choices.)
A.
Next Header
B.
Pad Length
C.
Padding
D.
Security Parameter Index
E.
Sequence Number
Explanation:
The Security Parameter Index (SPI) and Sequence Number fields make up the header of an Encapsulating
Security Payload (ESP) packet. ESP is an IP Security (IPSec) protocol that provides data integrity and
confidentiality for IP traffic. The ESP header is always part of the authenticated data in an ESP packet, but the
ESP header itself is never encrypted. By contrast, the ESP trailer, which is made up of the Padding, Pad
Length, and Next Header fields, is always part of the authenticated data and is always encrypted. The following
diagram illustrates the ESP packet format:
ESP can operate in transport mode or tunnel mode. In transport mode, ESP encrypts only the original payload
data and the resultant ESP trailer, leaving the original IP header unencrypted. The following diagram illustrates
the components of an ESP packet in transport mode:
In tunnel mode, ESP encrypts the entire packet, including the original IP header, the original payload data, and
the resultant ESP trailer. The following diagram illustrates the components of an ESP packet in tunnel mode:
IETF: RFC 4303: IP Encapsulating Security Payload (ESP): 2. Encapsulating Security Payload Packet Format
