NSE7_CDS_AR-7.6 Exam Dumps : Fortinet NSE 7 - Public Cloud Security 7.6.4 Architect

Comprehensive and Detailed Explanation From FortiOS 7.6, FortiWeb 7.4 Exact Extract study guide:

In an AWS SD-WAN Transit Gateway (TGW) Connect topology, traffic flow must be meticulously orchestrated through VPC route tables to ensure that the FortiGate-VM (Security VPC) can inspect traffic transitioning between spokes.

Spoke to TGW Redirection (Option E): For traffic to leave a Spoke VPC and reach the inspection hub, the Spoke VPC internal routing table must be configured to send all non-local traffic (0.0.0.0/0) to the Transit Gateway (TGW). This is the first step in the traffic chain.

TGW to FortiGate Redirection (Option A): Once the traffic arrives at the TGW and is forwarded to the Security VPC via a TGW attachment, it lands in the TGW subnet (or attachment subnet). To ensure this traffic is inspected, the Security VPC TGW subnet routing table must point the default route (0.0.0.0/0) to the FortiGate's internal network interface (ENI).

FortiGate Return/Egress Path (Option D): After the FortiGate processes the packet, it must be sent back to the TGW to reach its final destination in a different spoke or to exit via a different gateway. Therefore, the Security VPC FortiGate internal subnet routing table (the subnet where the FortiGate's internal leg resides) must have a default route (0.0.0.0/0) pointing back to the TGW.

Why other options are incorrect:

Option B: If the Security VPC TGW subnet routing table points to the TGW as the next hop, it creates a routing loop where traffic arrives from the TGW and is immediately sent back without being inspected by the FortiGate.

Option C: Pointing all traffic to an Internet Gateway (IGW) would bypass the Transit Gateway entirely and send traffic to the public internet rather than through the internal security fabric.

Comprehensive and Detailed Explanation From FortiOS 7.6, FortiWeb 7.4 Exact Extract study guide:

Based on the FortiOS 7.6 Cloud Security Study Guide regarding AWS Transit Gateway (TGW) integration and VPC routing, the following steps are mandatory to establish connectivity between Spoke VPCs via a TGW:

VPC Route Table Configuration (Option A): For traffic to leave a VPC and reach the Transit Gateway, the VPC's subnet route table must have a specific entry. While the exhibit shows local routes for internal VPC traffic (192.168.50.0/24 and 192.168.100.0/24), any traffic destined for "outside" the local VPC (such as the other Spoke VPC) must be directed to the TGW. Adding a default route (0.0.0.0/0) with the TGW ID as the next hop ensures that all non-local traffic is forwarded to the Transit Gateway for processing.

TGW Association (Option B): Within the Transit Gateway itself, connectivity is managed through Associations and Propagations. An "Association" links a specific VPC attachment to a TGW route table. Without associating the two attachments (for Spoke VPC A and Spoke VPC B) to a TGW route table, the TGW will not know which route table to use to make forwarding decisions for packets arriving from those VPCs.

Why Option C is incorrect: Route propagation is used to automatically populate the TGW route table with the CIDR blocks of the attached VPCs. While propagation is a valid step for dynamic routing, Option C specifically mentions propagating a static summary range (192.168.0.0/16) which is not the standard automated mechanism; usually, you propagate the specific VPC CIDRs. Furthermore, without the Association (Option B), propagation alone does not allow the TGW to process incoming traffic from the attachment.

Why Option D is incorrect: Directing traffic to an Internet Gateway (IGW) would send the traffic to the public internet. This would not facilitate internal routing between the two Spoke VPCs via the Transit Gateway.