Which of the following is the correct diagram for an IPsec Authentication Header?
A.
Option A
B.
Option B
C.
Option C
D.
Option D
E.
Option E
Explanation:
Authentication header (AH)
The AH is intended to guarantee connectionless integrity and data origin authentication of IP datagrams. Further, it can optionally protect against replay attacks by using the sliding window technique and discarding old packets. AH protects the IP payload and all header fields of an IP datagram except for mutable fields, i.e. those that might be altered in transit. In IPv4, mutable (and therefore unauthenticated) IP header fields include TOS, Flags, Fragment Offset, TTL and Header Checksum. AH operates directly on top of IP, using IP protocol number 51. An AH packet diagram:
Field meanings:
Next header
Identifies the protocol of the transferred data.
Payload length
Size of AH packet.
RESERVED
Reserved for future use (all zero until then).
Security parameters index (SPI)
Identifies the security parameters, which, in combination with the IP address, then identify the security association implemented with this packet.
Sequence number
A monotonically increasing number, used to prevent replay attacks.
Authentication data
Contains the integrity check value (ICV) necessary to authenticate the packet; it may contain padding.
