Cisco 400-251 Exam: AH Header Fields

AH Header Fields

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Question

Which three fields are part of the AH header? (Choose three.)

Answers

Explanations

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A. B. C. D. E. F. G.

CFG.

AH (Authentication Header) is a protocol used to provide authentication, integrity, and non-repudiation to IP packets. It is one of the protocols used in IPsec (Internet Protocol Security) to provide security to IP traffic. The AH header is inserted between the IP header and the upper-layer protocol header.

The AH header contains several fields that provide various security features. The three fields that are part of the AH header are:

  1. SPI identifying SA: The Security Parameters Index (SPI) is a 32-bit value that identifies the Security Association (SA) used to protect the packet. An SA is a unidirectional logical connection between two endpoints that provides security services to IP traffic.

  2. Sequence Number: The Sequence Number field is a 32-bit value that is used to prevent replay attacks. A replay attack is an attack in which an attacker intercepts and retransmits packets to achieve some malicious purpose.

  3. Packet ICV: The Integrity Check Value (ICV) is a hash value that is used to verify the integrity of the packet. The ICV is calculated over the entire packet, including the AH header and the upper-layer protocol header.

Therefore, the correct answer is:

  • F. SPI identifying SA
  • C. Packet ICV
  • D. Protocol ID

A. Source Address, E. Application Port, and G. Payload Data Type Identifier are not part of the AH header. The Source Address is part of the IP header, while the Application Port and Payload Data Type Identifier are part of the upper-layer protocol header.