Start-up Company has 3 VPC created for a test setup. VPC A is peering with VPC B & VPC
C. VPC B& VPC C have the same CIDR block. There is a single instance in VPC B & 100+ instance in VPC
C. Instance in VPC A needs to communicate with an instance in VPC B & all instances in VPC
C. Which of the following routing can be used to meet this requirement?

Answer options:

A.Add a more specific routing entry for Instance in VPC A in the routing table of VPC B pointing to target as VPC Peering connection between VPC A & VPC
B.B.Add a more specific routing entry for Instance in VPC B in the routing table of VPC A pointing to target as VPC Peering connection between VPC A & VPC
B.C.Create a new VPC with separate subnets between VPC A & VPC
B.D.Add a less specific routing entry for Instance in VPC A in the routing table of VPC B pointing to target as VPC Peering connection between VPC A & VPC
B.

Correct Answer: B
VPC Route table selects routes based upon the longest prefix match. In the above case, VPC B & C have the same subnet. So, from VPC A to communicate with an instance in VPC B, a more specific route is added in the route table so that it will be preferred. For communication with instances in VPC C, less specific routes will be added. So communication can be established between instances in VPC A & all instances in VPC
C.Option A is incorrect as Since VPC B & VPC C share the same subnet, routing entry for a more specific instance in VPC B should be made in VPC A routing table & not in the VPC B routing table. Also, if VPC B is only peering with VPC A, more specific or less specific will not matter. But a routing entry should be added for all instances in VPC A.Option C is incorrect as Creating a new VPC with different subnets is not required as communication between instances in VPC B & VPC A can be achieved by routing changes.
Option D is incorrect as adding less specific routes for instance in VPC B will make VPC A prefer routes in VPC C over VPC
B.For more information on VPC Peering, refer to the following URL-
https://docs.aws.amazon.com/vpc/latest/peering/peering-configurations-partial-access.html