Cisco Certified Network Associate (CCNA) Practice Exam

Which feature helps to prevent replay attacks in IPsec communications?

1. Encryption Key Rotation

2. Anti-replay protection

3. Traffic Filtering

4. Data Compression

The correct answer is: Anti-replay protection

The feature that helps to prevent replay attacks in IPsec communications is anti-replay protection. This mechanism is integral to the security protocols used in IPsec, specifically within the Authentication Header (AH) and Encapsulating Security Payload (ESP) protocols. Replay attacks occur when an attacker captures a data packet and retransmits it later to gain unauthorized access or to disrupt communication. Anti-replay protection counters this threat by using a unique sequence number for each packet transmitted. The receiving side keeps track of the sequence numbers of recently received packets and can identify and discard any packet that appears again (i.e., a replay). This ensures that each packet is unique in the context of the current communication session, protecting against the reception of duplicated packets. The other features listed do not specifically address the issue of replay attacks. For example, encryption key rotation helps to enhance the overall security of cryptographic keys but does not directly prevent replay attacks. Traffic filtering focuses on controlling the flow of packets based on predefined rules, and data compression reduces the size of the payload, neither of which impacts the fundamental need to ensure the uniqueness of each transmitted packet within a session.