H12-711_V4.0 Exam Dumps : HCIA-Security V4.0 Exam

Explanation From HCIA-Security documents:

In IKEv1 Phase 1 aggressive mode, the negotiation completes in three messages, unlike main mode which uses six.

Message 1 (Initiator → Responder): Contains the IKE proposal, Diffie-Hellman public value, nonce, and the initiator’s identity information.

Message 2 (Responder → Initiator): Returns the selected proposal, responder’s Diffie-Hellman public value, nonce, identity information, and authentication data. At this stage, the initiator can authenticate the responder.

Message 3 (Initiator → Responder): Carries the initiator’s authentication data, allowing the responder to verify and authenticate the initiator.

Therefore, the primary function of message 3 is to provide authentication information so that the responder can confirm the identity of the initiator.

Options A and B correspond to earlier negotiation steps, and C describes part of message 2. Hence, the correct answer is D.

Explanation From HCIA-Security documents:

This scenario states two key conditions: (1) there are only a small number of users accessing the Internet, and (2) the number of available public IP addresses is equal to the number of concurrent Internet users. That means the organization has enough public addresses to assign a dedicated public IP to each internal user at the same time. In such a case, the most suitable NAT type is NAT No-PAT, which is also commonly understood as traditional one-to-one address translation (no port translation). The internal source IP is translated to a unique public source IP, and the transport-layer port number is not multiplexed to share a single public IP among many users.

By contrast, NAPT and Easy IP are used when public addresses are scarce, because they translate multiple internal users to one or a few public IP addresses by also translating port numbers (PAT). 3-tuple NAT is a more specific translation method involving matching/translation with additional parameters, but it is not the standard choice described by the given “equal number of public IPs and concurrent users” condition. Therefore, NAT No-PAT is correct.