So I just failed the CSA Pro 2019 exam and I’m taking another shot at it. One of the questions that stuck in my mind was about 3 VPCs peered together (B & C to A). VPC B and VPC C have overlapping CIDRs. I am pretty sure this is the exact image used from the exam – https://docs.aws.amazon.com/vpc/latest/peering/images/one-to-two-vpcs-lpm-diagram.png
(That image is from here, near the bottom – https://docs.aws.amazon.com/vpc/latest/peering/peering-configurations-partial-access.html)
So the situation involved only needing to route from VPC A to VPC B to get to the one instance, but still needing access to all of VPC C .
I totally guess at the answer, I think I picked an answer that mentioned a specific route for the instance in VPC B? I am not very strong in this area, if it isn’t obvious. Even reading over the AWS documentation is just confusing to me. I think the documentation tells me that I picked the right answer since I only remember one answer mentioning a specific route for the instance in VPC B.
hey Josh, sorry to hear you didn’t make it. My exam is this Saturday and your post will be helpful for me. Aside from this VPC question, could you share more tips about the exam? I know there will be lots of AWS Organizations, Systems Manager, Shield/WAF/Config questions but would like to know more from you who recently took it.
Thanks for posting this question, I ended up getting a 730 and didn’t have time to break this question down. Frustrated but hopefully it comes up on my next attempt. Basically you want /32 to declare the individual IP you want in B, and then the full subnet from C pointing to the /16. Pretty sure this breaks down to most specific route wins "VPC route tables use longest prefix match to select the most specific route across the intended VPC peering connection. All other traffic is routed through the next matching route, in this case, across the VPC peering connection pcx-aaaacccc."
Hey Josh, I just want to thank you again for sharing your tips. I passed my AWS SA Pro exam, all thanks to this post! I am so happy!
Here is my exam feedback: