AH: Authentication Header Protocol | Cisco 400-251 Exam

Authentication Header Protocol

Prev Question Next Question


Which statement about the AH is true?



Click on the arrows to vote for the correct answer

A. B. C. D. E.


AH stands for Authentication Header, which is one of the protocols used in IPsec to provide integrity, authentication, and anti-replay protection to IP packets. It is responsible for authenticating the entire IP packet, except for any mutable fields, by adding a header to the original packet.

Mutable fields are those fields in the IP packet that can be modified while the packet is in transit, such as the TTL (time to live) or the IP header checksum. AH does not protect these fields because their modification is expected as the packet travels across the network.

Based on the given options, the correct answer is (E) "AH authenticates the entire packet except for any mutable fields." This means that AH provides authentication for all non-mutable fields, including the IP header and the data payload, but does not protect mutable fields.

Option (A) is incorrect because AH provides authentication for the entire packet, not just the data. Option (B) is incorrect because AH authenticates the IP header as well as the data. Option (C) is incorrect because AH does not authenticate only the TCP-UDP header, but the entire packet. Option (D) is partially correct because AH authenticates the entire packet, including mutable fields, but it does not protect mutable fields.