Which of the following is the best use case of a site-to-site VPN?

A site-to-site VPN is used to securely connect two networks over an untrusted network, most commonly the public internet. In Network+ (N10-009) objectives, VPNs are described as providing confidentiality and integrity for data in transit by creating an encrypted tunnel between sites (for example, headquarters and a branch office). This allows systems at both locations to communicate as if on the same private WAN, while preventing eavesdropping or tampering by intermediate networks. Typical implementations use IPsec tunneling and rely on negotiated encryption/authentication parameters to protect traffic end-to-end between VPN gateways.

Encrypting data at rest refers to storage encryption (disk/database), not VPN tunneling. Filtering traffic between two internal subnets is usually handled by ACLs, firewalls, or segmentation controls, not a site-to-site VPN. Hosting public-facing applications is a DMZ / reverse proxy / WAF design concern; a VPN is not the primary control for exposing public services (and generally you would not require the public to use a VPN to reach a public website). Therefore, securing site connectivity across an untrusted network is the best match.

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