A SysOps Administrator is troubleshooting a connectivity issue between two VPCs in the us-east-1 Region. VPC A has a CIDR block of , and VPC B has a CIDR block of . Both VPCs are attached to an AWS Transit Gateway. Amazon EC2 instances in VPC A are unable to communicate with EC2 instances in VPC B. The security groups and network ACLs in both VPCs allow all traffic. Which of the following routing configuration steps must the SysOps Administrator perform to resolve this connectivity issue? (Select TWO.)
- Add a route in the VPC A subnet route tables with a destination of targeting the Transit Gateway, and a route in the VPC B subnet route tables with a destination of targeting the Transit Gateway.Answer
- Ensure the Transit Gateway route table contains routes for pointing to the VPC A attachment and pointing to the VPC B attachment.Answer
- CAdd a route targeting the Internet Gateway in the VPC A subnet route tables with a destination of .
- DEnable route propagation in the VPC subnet route tables to automatically discover the CIDR block of the peered VPC.
- EDeploy a NAT Gateway in each VPC and update the subnet route tables to route all cross-VPC traffic through the NAT Gateway.
Answer
Add a route in the subnet route tables of both VPCs targeting the Transit Gateway, and ensure the Transit Gateway route table has routes for both VPC CIDR blocks pointing to their respective attachments.
To establish two-way communication between two VPCs attached to a Transit Gateway, you must update routing at both layers: the VPC subnet route tables and the Transit Gateway route table. First, each VPC subnet route table needs a route for the remote VPC CIDR block targeting the Transit Gateway. Second, the Transit Gateway route table must have routes mapping each VPC CIDR block to its respective Transit Gateway attachment.
Step-by-Step Solution
Key Concept
VPC routing via Transit Gateway requires updating both the VPC subnet route tables and the Transit Gateway route tables.