Comprehensive and Detailed 200 to 250 words of Explanation From HCIP Datacom Campus Network documents knowledge without any URL or Links:
Encapsulating Security Payload (ESP) is one of the core IPsec protocols used to protect data confidentiality, integrity, and authenticity. To prevent replay attacks, ESP includes aSequence Numberfield in its header. This field plays a critical role in ensuring packet freshness.
Each ESP packet carries a monotonically increasing sequence number assigned by the sender. The receiving device maintains a sliding window and checks incoming packets against this window. If a packet arrives with a sequence number that has already been received or falls outside the valid window, the packet is considered a replay and is discarded. This mechanism effectively protects the network against replay attacks, where attackers capture legitimate packets and retransmit them to disrupt communication or bypass security controls.
TheSPI (Security Parameters Index)identifies the security association used for the packet but does not provide replay protection. TheNext Headerfield indicates the type of payload carried in the ESP packet.Authentication Dataensures packet integrity and data origin authentication but does not independently prevent replay attacks without the sequence number mechanism.
According to HCIP Datacom Campus Network documentation and IPsec standards, replay protection in ESP is implemented using the Sequence Number field, making option A the correct answer.
