Within the Encrypted Security payload (ESP) extension header, which of the following identifies
the encryption association?

A.
Security Parameters Index (SPI)

B.
Payload Type.

C.
Padding.

D.
Sequence Number.

Explanation:
By combining the SPI with the destination address and the Security Protocol (ESP) identifies the
security association of the packet. The SPI is an unsigned 32-bit integer.
Incorrect Answers:
B: The ESP header does not have a field called the payload type. There is payload data and
payload length, for the length of the payload. The type of payload is actually stored in the next
header field.

C: Padding are the characters added after the data payload. The number of padding characters is
determined by a pad length. Padding is used to control the size and alignment of the message.
The Pad Length indicates the number of 8-bit passing bytes to be added after the data. The
padding ensures the message ends on a 64-bit boundary.
D: The sequence number is used for anti-replay.