Zero Trust Principles: Require explicit, identity-based access controls at every network stage. Evaluate OCI Services: Internet Gateway: Enables public internet access, no identity-based control. Service Gateway: Provides private service access, no granular routing control. NSGs: Offer stateful, identity-based rules at the VNIC level. DRG: Facilitates routing, not identity-based access control. NSG Fit: NSGs allow rules based on VNIC identity, source/destination IP, and ports, aligning with Zero Trust. Conclusion: NSGs are the best fit for granular, identity-based routing control. NSGs are pivotal for Zero Trust in OCI. The Oracle Networking Professional study guide states, "Network Security Groups provide granular, stateful security rules that can be applied to specific VNICs, enabling identity-based access controls essential for Zero Trust architectures" (OCI Networking Documentation, Section: Network Security Groups). Unlike security lists (subnet-level), NSGs offer instance-level precision. Reference: Oracle Cloud Infrastructure Documentation - Network Security Groups.

Analyze Connectivity Successes: Instance A can ping its subnet gateway (10.0.1.1), indicating that local subnet routing and security rules are functioning for IPv4. It can also ping Instance B’s IPv6 address (fc00:1:2::20), confirming that IPv6 routing and security rules between subnets are operational. Identify the Failure: Instance A cannot ping Instance B’s IPv4 address (10.0.2.20). Since security lists and NSGs allow all traffic, the issue is unlikely to be a security configuration problem. Examine Routing for Instance A: The route table for Instance A’s subnet (10.0.1.0/24) has a rule directing traffic to 10.0.2.0/24 via the VCN Local Peering Gateway (LPG). In OCI, LPGs are used for intra-region VCN peering, but here, both instances are in the same VCN, so this rule is likely a misconfiguration or irrelevant unless peering is involved. However, the successful IPv6 ping suggests basic connectivity exists. Check Return Path from Instance B: For a ping to succeed, Instance B must send ICMP replies back to Instance A (10.0.1.10). Instance B’s subnet (10.0.2.0/24) needs a route table entry to send traffic to 10.0.1.0/24. Without this, replies are dropped, causing the IPv4 ping to fail. The IPv6 success indicates that IPv6 routing is correctly configured both ways, possibly via SLAAC or default routes. Evaluate Options: A: Incorrect. IPv6 is enabled, as Instance A pings Instance B’s IPv6 address. B: Correct. Missing route for 10.0.1.0/24 in Instance B’s subnet prevents IPv4 replies. C: Incorrect. Security lists and NSGs can filter IPv6 traffic in OCI. D: Incorrect. Ping supports IPv6, as evidenced by the successful IPv6 ping. The most probable cause is a missing route in Instance B’s subnet route table. In OCI, each subnet has its own route table, and for instances in different subnets within the same VCN to communicate, both subnets must have appropriate routes. The successful IPv6 ping suggests that IPv6 routing is intact (likely due to default behavior or SLAAC), but IPv4 requires explicit routing. Per the Oracle Networking Professional study guide, "Route tables must be configured to direct traffic to the appropriate next hop for inter-subnet communication within a VCN" (OCI Networking Documentation, Section: Virtual Cloud Networks). Reference: Oracle Cloud Infrastructure Documentation - Networking Overview, Route Tables.

Requirement Analysis: The solution must ensure private access to Object Storage without public internet traversal, while being cost-effective. Evaluate OCI Components: Internet Gateway: Provides public internet access, unsuitable for private connectivity. NAT Gateway: Allows outbound internet access from private subnets, but traffic still exits OCI. Service Gateway: Enables private access to OCI services like Object Storage within the same region. DRG with FastConnect: Used for on-premises connectivity, not intra-OCI service access. Option Assessment: A: Uses public internet, violating the security policy. B: HTTPS encrypts data, but traffic traverses the internet via NAT, violating the policy. C: Service Gateway keeps traffic within OCI’s private network, meeting security and cost goals. D: Overly complex and costly, with public endpoints contradicting the requirement. Conclusion: Service Gateway with regional Object Storage endpoints ensures private, secure, and costeffective access. The Service Gateway is designed for private access to OCI services like Object Storage, avoiding the public internet. The Oracle Networking Professional study guide states, "A Service Gateway allows instances in a private subnet to access supported OCI services without an Internet Gateway or NAT Gateway, ensuring traffic remains within the Oracle network" (OCI Networking Documentation, Section: Service Gateway). Using the Oracle Services Network service CIDR label for the region ensures compatibility with Object Storage endpoints, optimizing cost and security. Reference: Oracle Cloud Infrastructure Documentation - Service Gateway.