Exam CV0-003 topic 1 question 16 discussion

Explanation: The cloud architect needs to design a highly available and scalable VPC setup that can handle 60 nodes per region while accounting for reserved IP addresses. Subnet Sizing Considerations: A /24 subnet provides 256 IP addresses (from .0 to .255). A /25 subnet provides 128 IP addresses (from .0 to .127 or .128 to .255). A /26 subnet provides 64 IP addresses, but 5 are reserved for network, broadcast, and cloud provider reservations, leaving only 59 usable IPs, which is insufficient for 60 nodes per region. A /27 subnet provides 32 IP addresses, which is far too small.

B. Create three /25 subnets in different regions. Here's the breakdown: High availability: Having subnets in different regions ensures that the application remains available even if one region goes down. Horizontal auto-scaling: This ensures the system can scale out by adding more instances as needed. 60 nodes peak capacity per region: A /25 subnet provides 128 IP addresses, but with 5 reserved, that leaves 123 usable IP addresses. This comfortably accommodates the 60 nodes. Five reserved network IP addresses per subnet: The calculation leaves enough IP addresses in a /25 subnet for the required nodes. Using three subnets ensures distribution across multiple regions, enhancing high availability and redundancy. It also maintains the necessary capacity and supports horizontal auto-scaling.

2^(number of host bits) = # of addresses ex. /24 means there are (32 -24) 8 host bits. 2^8 = 256 /26 subnets only have 64 addresses. With 5 reserved addresses that means they only have 59 usable addresses. This is insufficient for the question requirement of 60 nodes per region. /27 subnets only have 32 addresses. similarly insufficient. That leaves only /25 subnets A. Create two /25 subnets in different regions. Each subnet has 128 IP addresses, but with five reserved addresses, the usable IP addresses would be 123. The total available capacity across both subnets would be 2 * 123 = 246. B. Create three /25 subnets in different regions. Similar to option A, each subnet has 128 IP addresses, but with five reserved addresses, the usable IP addresses would be 123. The total available capacity across three subnets would be 3 * 123 = 369 The question does not concern itself with cost, overheard, complexity, or performance. Since it asks for what BEST fits the requirements, I will say option B provides slightly more capacity and fault tolerance with an additional subnet.

The "Create two/three" and the "HA" and "horizontal scaling" threw me off. Requirements: 60 IPs total (per region), 5 reserved IPs (per subnet) /27 gives you 30 IPs. Since the reserved IPs are taken PER subnet, it'll be 25 per subnet. If you make 3 of these, you have 75 IPs for the nodes.

E. Five reserve network IP addresses per subnet denotes /27 (/25 yields 2, /26 yields 4 & /27 yields 8 meaning a /27 is required for 5 network IP from the subnetted /24) 60 nodes peak capacity per region means you need two /27 with 30 usable each by giving 5 bits to the host field. ( 1 yields 2, 2 yields 4, 3 yields 8, 4 yields 16 and 5 yields 32. Minus two IPs for the network and broadcast leaving 30.) Two of these would be peak capacity of 60. Answer is two /27 subnets in different regions.

You need 65 IPs per region. /27 will only give you 32 and /26 will only give you 64. You need a /25 network which will give you 128 per region. Having two regions will give you the requirement of high availability. Yes, 3 regions is better than 2, but it doesn't ask for the best high availability option, it just asks for high availability which 2 regions provides.

The requirement of 60 nodes peak capacity per region suggests that the solution should be designed for scalability. Additionally, the requirement of high availability indicates that the solution should be distributed across multiple regions. Each subnet should have at least five reserved network IP addresses. This leaves 251 addresses per subnet in a /24 range. To meet these requirements, the BEST solution would be to create three /26 subnets in different regions. This would provide a total of 753 IP addresses per region (3 subnets x 251 IP addresses per subnet) and allow for horizontal auto-scaling up to 60 nodes per region. Having three subnets per region would provide redundancy and high availability.

A is correct

To meet the above requirements, the best option would be to create two /26 subnets in different regions (Option C). A /24 network range provides 256 IP addresses, which would be too large for the requirements of 60 nodes peak capacity per region and five reserved network IP addresses per subnet. A /26 subnet provides 64 IP addresses, which is a better fit for the requirements. With two /26 subnets in different regions, the architect can ensure high availability through load balancing and auto-scaling by allocating the IP addresses dynamically. Additionally, two subnets provide ample space for five reserved IP addresses and 60 nodes peak capacity per region. Options A, B, E, and F would provide either too few or too many IP addresses to meet the requirements, so they are not the best choices.

Correct answer is A

"A" would be the correct answer for this scenario on the premise: HA is guaranteed through the horizontal scaling, allowing different subnets in different regions. With 60 nodes (IP addresses), you can count out the /26 (64 available IPs, when you need 5 IPs in reserve) and /27 (32 available IPs aren’t enough). And finally, it is physically impossible to create three /25 subnets due to IPs multiplying/dividing in increments of 2 (i.e., /25 = 128 and /24 = 256).

So if the question states ony having a /24 to work with it would have to A