Exam ANS-C00 All Questions

View all questions & answers for the ANS-C00 exam

Exam ANS-C00 topic 1 question 246 discussion

Exam question from Amazon's ANS-C00

Question #: 246
Topic #: 1

Your company just acquired a new company. You have two VPCs ?one is 172.31.0.0/16 and one is 10.111.0.0/16. The acquired company uses 10.111.0.0/16 for their VPC. Your VPC "A" has a group of 12 servers in the range 10.111.2.101 ?10.111.2.112. Their VPC "B" has 20 servers from 10.111.2.171 ?10.111.2.190.
You need to access both VPCs from the 172.31.0.0/16 VPC "C".
What is the best way to approach this problem?

A. From VPC C, create a peering connection and add a route to VPC A's peering connection for 10.111.2.96/27 and a route to VPC B's peering connection for 10.111.2.0/24.
B. From VPC C, create a peering connection and add a route to VPC A's peering connection for 10.111.2.96/28 and a route to VPC B's peering connection for 10.111.2.0/24.
C. From VPC C, create a peering connection and adjust the route tables to direct traffic to the individual servers by exact IP address of the servers.
D. Invest the money and change the CIDR of one of the VPCs since one VPC cannot be peered to two VPCs with the same CIDR block.

Show Suggested Answer

Suggested Answer: A 🗳️
You can peer VPCs with the same CIDR block to a third VPC, so changing the CIDR block is not necessary. You can adjust the route tables to point to individual servers, but this would be very inefficient. 10.111.2.96/28 does not provide enough addresses for the AWS required addresses. AWS reserves 5 addresses per subnet and this only allows 11 addresses. 10.111.2.96/27 provides 32 addresses with 27 usable. Since it is a /27, it will take precedence over the /24 and route the traffic destined for these instances correctly.

by awspro2021 at March 12, 2021, 1:27 p.m.

Disclaimers:

- ExamTopics website is not related to, affiliated with, endorsed or authorized by Amazon.
- Trademarks, certification & product names are used for reference only and belong to Amazon.

Comments

Submit Cancel

awspro2021

Highly Voted 3 years, 8 months ago

A - is correct VPC A = .96/27 = 32 IPs ; VPC B x.x.0/24 256 IPs B - wrong VPC A = .96/28 = 16 IPs ; VPC B x.x.0/24 256 IPs , can't use the last ip in vpc for the server, as is it reserved for Broadcast.

upvoted 10 times

thulasi39

3 years, 8 months ago

D is the right answer, then?

upvoted 2 times

...

walkwolf3

Most Recent 3 years, 7 months ago

Go with A

upvoted 1 times

...

ptpho

3 years, 7 months ago

I think It's A In C you need 2 peering not 1, and we are asking about route between VPCs not VPC to servers through peering

upvoted 3 times

...

namirmatar

3 years, 7 months ago

I think B is a better answer, since the CIDR is used for routing and not for VPC so there are no reserved IPs, it's a notation, same as if you want to route to a specific destination you would write 10.111.2.96/32

upvoted 3 times

namirmatar

3 years, 7 months ago

After reviewing my answer, I think A is correct but not because AWS reserves 5 addresses, this has nothing to do with it. It is because you start counting from 96 so 10.111.2.96/28 will designate these 16 addresses .96 .97 .98 .99 .100 .101 .102 .103 .104 .105 .106 .107 .108 .109 .110 .111 so the server with the address .112 will not be reached.

upvoted 9 times

Alberto_M_M

3 years, 7 months ago

This is the correct answer. You have to use two static routes. One (/27: more specific) for the VPC-A and other (/24: less specific) for VPC-B. This is the best practice.

upvoted 1 times

sapien45

3 years, 2 months ago

Two best answers of this topic

upvoted 1 times

...

ChauPhan

3 years, 8 months ago

Route tables at VPC C 1. For 10.111.2.96/27 -> VPC A: IP from 10.111.2.96 to 10.111.2.128 covers 12 servers of VPC A 2. For 10.111.2.0/24 -> VPC B, IP from 10.111.2.0 --> 10.111.2.255: covers servers of VPC-B 1st route 10.111.2.96/27 is more specific, it will route to VPC-A Otherwise, it will route to VPC-B

upvoted 3 times

ChauPhan

3 years, 8 months ago

B. From VPC C, create a peering connection and add a route to VPC A's peering connection for 10.111.2.96/28 and a route to VPC B's peering connection for 10.111.2.0/24.

upvoted 1 times

ChauPhan

3 years, 8 months ago

10.111.2.96/28, 2^5 = 32, 10.111.2.96 --> 10.111.2.128

upvoted 1 times

ChauPhan

3 years, 8 months ago

Sorry wrong /28 ~ 2^4 = 16 not correct

upvoted 1 times

...

Nimolee

3 years, 8 months ago

C is correct. In routing, you always want to be specific about the destination in your routes. Although A and B both works, it's not the best practice.

upvoted 2 times

...