Subnets
Subnets are smaller, individual sections of a VPC IP address range partitioned into different availability zones for redundancy and fault tolerance. They segregate network traffic, allowing for better application performance and security. Subnets can be either private or public, depending on whether they have direct access to the internet via an Internet Gateway (IGW). While private subnets only allow internal access, public subnets can be accessed from the internet.
Guide: Answering Questions on Subnets in Amazon VPC for the AWS Solution Architect exam
What is a Subnet? - Importance
A subnet, or subnetwork, is a division of a network where you can allocate a part of the IP address range of your network to a subnetwork. In Amazon VPC, a subnet functions the same way, allowing users to divide their VPC's IP address range into different ranges, each representing a different subnet.
Subnets are critically important because they provide better organization, security, and traffic management within a VPC. Having subnets allows us to isolate system parts from one another, thereby limiting the impacts of potential faults, and making the system more reliable.
How It Works
Each subnet you create is linked to an Availability Zone, thereby increasing fault tolerance and low latency. It's recommendable to establish multiple subnets in different availability zones to ensure system reliability and fault tolerance.
Exam Tips: Answering Questions on Subnets
1. Understand the purpose and function of a subnet: This is key to answering all subnet-related questions. Know when and why you would use a subnet within a VPC.
2. Familiarize yourself with default and non-default VPCs and subnets: AWS creates a default VPC and subnet for users to use right away. A default VPC has a size /16 IPv4 CIDR block, and each default subnet has a size /20 default IPv4 CIDR block. Understanding the differences can help you answer the questions.
3. Know how to calculate the number of subnets: Questions may ask you to calculate how many subnets or hosts-per-subnet can be created within a CIDR block. Remember, the number of subnets depends on the number of bits borrowed to identify the subnet.
AWS Certified Solutions Architect - Amazon VPC Example Questions
Test your knowledge of Amazon Simple Storage Service (S3)
Question 1
You are designing an AWS VPC for a client who requires to host services within four private subnets. However, the client wants to minimize the number of allocated IP addresses in each subnet. What is the smallest subnet size you can create?
Question 2
Your company requires that instances within a public subnet in a VPC must be reachable from the internet. The instances have public IPs, and the security groups and NACLs are configured to allow incoming and outgoing traffic. However, the instances are still not reachable. What is the most likely cause?
Question 3
You have deployed multiple applications in a shared VPC across several subnets, each belonging to a different department. The accounting department's application has compliance requirements which demand that their data must not traverse the public internet. How should you ensure that data in their subnet meets this requirement?
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