What is a CIDR in VPCs and AWS?

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My understanding is that you can launch subnets (a collection of IP addresses) in a VPC (a network that you set up), and that CIDRs… do what?

I’m not entirely sure what a subnet or a VPC is, either. I don’t know how they all play together.

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4 Answers

Anonymous 0 Comments

CIDR stands for Classless Inter-Domain Routing. It is a fancy term for subnetting. Classful network addresses follow standardized rules for what part of the IP address specifies the network ID and what part specifies the host ID. Similar to mailing adresses, the network ID would be the street name and the host id is the house number. Subnetting is a way to modify what part is the network id and what is the host id.

VPC is a product/service within AWS. You are renting a virtual network environment. You can use it to set up your own virtual services. With that you can design your own internal IP address scheme within your network. You can follow classful network rules if you want to or you can create subnets to give yourself more granular control over your network traffic.

Anonymous 0 Comments

the CIDR simply tells you how many addresses are available when you set a certain subnet mask.

For example a /24 gives you 254 available addresses (256 but the first and the last bit is unavailable, they are the network and the broadcast address respectively).

The /24 mask is [`255.255.255.0`](https://255.255.255.0) which means the last set of numbers equals 256 available addresses. It is usefull to set up smaller networks and not use up a huge numbers of ip-addresses that would go unused if all you need is a maximum of 254.

Anonymous 0 Comments

the CIDR simply tells you how many addresses are available when you set a certain subnet mask.

For example a /24 gives you 254 available addresses (256 but the first and the last bit is unavailable, they are the network and the broadcast address respectively).

The /24 mask is [`255.255.255.0`](https://255.255.255.0) which means the last set of numbers equals 256 available addresses. It is usefull to set up smaller networks and not use up a huge numbers of ip-addresses that would go unused if all you need is a maximum of 254.

Anonymous 0 Comments

CIDR stands for Classless Inter-Domain Routing. It is a fancy term for subnetting. Classful network addresses follow standardized rules for what part of the IP address specifies the network ID and what part specifies the host ID. Similar to mailing adresses, the network ID would be the street name and the host id is the house number. Subnetting is a way to modify what part is the network id and what is the host id.

VPC is a product/service within AWS. You are renting a virtual network environment. You can use it to set up your own virtual services. With that you can design your own internal IP address scheme within your network. You can follow classful network rules if you want to or you can create subnets to give yourself more granular control over your network traffic.