Hello, I'm going to give a very brief introduction to the VPC or the Virtual Private Cloud. It's not an area that we need to know in detail for Cloud Practitioner but we do need to be aware of some of the terminology. The Virtual Private Cloud is a core building block for designing highly available, fault-tolerant environments. Since 2013, all accounts have a Virtual Private Cloud by default. Now the Virtual Private Cloud, or VPC, is a logically isolated section of the AWS Cloud dedicated to your environment. You have complete control over the VPC including the IP range, subnets, routing tables and security. VPCs use security groups and access control lists to secure access and protect against unauthorized entry access. 

Subnets are CIDR blocks within the IP range of your VPC. What's a CIDR block, I hear you ask? That stands for Classless Inter-Domain Routing. It's essentially a block of IP numbers. In short, the VPC is your private CIDR block of the AWS cloud. You can have a CIDR of 16 down to a CIDR of 28. Let's look at the core components and acronyms of the VPC. Subnet is a segment of the VPC's IP address range where you can place groups of isolated resources. The IGW is a great acronym to forget in the last five minutes of an exam. It's the Internet Gateway, the Amazon VPC side of a connection to the public internet. Hardware VPN connection is a hardware-based VPN between your Amazon VPC and your data center or co-load facility. VGW is another great one to forget when you see it written down on the question. VGW stands for the Virtual Private Gateway and that's the Amazon VPC side of a VPN connection. With Virtual Private Gateways, you can connect existing networks to your VPC. 

How about CGW? Customer Gateway, your side of a VPN connection. So routers interconnect subnets and direct traffic between Internet Gateways, Virtual Private Gateways, Net Gateways, and subnets. Peering connections enable user route traffic via private IP addresses between two peered VPCs. The first four IP addresses and the last address of any subnet are not available. Now these are reserved by AWS for routers, DNS, broadcast and network addresses. AWS won't allow you to create netmasks lower than /16 or higher than /28. Each subnet must be associated with a route table. Every subnet that you create is automatically associated with the main route table for the VPC. Each subnet must be associated with a network access control list. If you don't explicitly associate a subnet with a network access control list, the subnet is automatically associated with a default network access control list. That concludes this short lecture on the VPC, the Virtual Private Cloud.