Layer 3 secure tunneling standard: Which option describes the industry-standard suite that secures data over IP networks at the OSI Network layer (Layer 3)?

Introduction / Context:
Secure site-to-site and remote-access connectivity often relies on standards at Layer 3. The question differentiates between a generic concept (VPN) and the specific standardized protocol suite used to implement secure IP-layer protection.

Given Data / Assumptions:

• OSI Network layer (Layer 3) focus.
• Looking for an industry-wide standard suite, not merely a service concept.
• Transport medium may be the public Internet or private IP networks.

Concept / Approach:
IP Security (IPSec) is a suite of protocols (AH, ESP, and related key management like IKE) providing confidentiality, integrity, and authentication at Layer 3. While VPN is the broader concept of creating private networks over shared infrastructure, IPSec is the standard mechanism used at the IP layer to realize that goal.

Step-by-Step Solution:

Verification / Alternative check:
Standards documents define IPSec operating at the IP layer, independent of applications, protecting any IP traffic.

Why Other Options Are Wrong:
VPN: A concept; can be implemented via IPSec, SSL/TLS, GRE+IPSec, etc.
HDLC/Cable/xDSL: Physical/link-layer technologies without built-in IP-layer security suite.

Common Pitfalls:
Equating the service name 'VPN' with a specific protocol suite. Always distinguish the concept from the implementing protocols.

Final Answer:
IPSec