You have 2 VPC’s , VPC A and VPC
B. Both the VPC’s have been peered. You have configured the route tables in VPC A so that traffic can flow from VPCA to VPCB. You try to ping an instance in VPCB from VPCA , but are unable to do so. You have confirmed that the NACL’s and Security Groups have been configured properly. What could be the reason for this issue?

Answer options:

A.The VPC’s have overlapping CIDR blocks
B.Security Groups don’t work in peered VPC’s hence the requests will not work.
C.NACL’s don’t work in peered VPC’s hence the requests will not work.
D.The route tables in VPCB have not been configured.

Answer – D
The AWS Documentation mentions the following
To send traffic from your instance to an instance in a peer VPC using private IPv4 addresses, you must add a route to the route table that`s associated with the subnet in which the instance resides. The route points to the CIDR block (or portion of the CIDR block) of the other VPC in the VPC peering connection.
The owner of the other VPC in the peering connection must also add a route to their subnet`s route table to direct traffic back to your VPC.For more information on VPC Peering routing, please visit the below URL:
http://docs.aws.amazon.com/AmazonVPC/latest/PeeringGuide/vpc-peering-routing.html