What is the purpose of the sequence number in the ESP or AH header?
A.
Provide protection for missing packets that have been encrypted
B.
Provide protection from someone trying to reply captured data later in the session
C.
Provide protection from hackers changing the sequence number in the layer 4 header
D.
Provide protection from someone trying to resequence the packets to try and crash the system
Explanation:
IPsec uses two different protocols – AH and ESP – to ensure the authentication, integrity and confidentiality of the communication. It can protect either the entire IP datagram or only the upper-layer protocols. The appropiate modes are called tunnel mode and transport mode. In tunnel mode the IP datagram is fully encapsulated by a new IP datagram using the IPsec protocol. In transport mode only the payload of the IP datagram is handled by the IPsec protocol inserting the IPsec header between the IP header and the upper-layer protocol header. The 32 bit Sequence Number protects against replay attacks.