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AWS VPC Subnet Planning: Best Practices for /24 to /28 Networks

By Yurlie Architecture Team•August 3, 2026•7 min read

Understanding AWS IP Address Reservations

When you provision a subnet in AWS, the platform automatically reserves five IP addresses within every CIDR block. You cannot assign these reserved addresses to Amazon EC2 instances, Application Load Balancers, or container tasks.

For a standard /24 subnet containing 256 total IP addresses (from 10.0.1.0 to 10.0.1.255), AWS reserves the following:

10.0.1.0: Network address.
10.0.1.1: Reserved by AWS for the VPC router.
10.0.1.2: Reserved by AWS for Domain Name System (DNS) resolution.
10.0.1.3: Reserved by AWS for future functionality.
10.0.1.255: Network broadcast address.

Consequently, a /24 CIDR block yields exactly 251 usable IP addresses rather than the theoretical 254.

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Subnet Size Allocation Reference Table

CIDR Prefix	Subnet Mask	Total IP Count	Usable AWS Hosts	Recommended Deployment Role
/16	255.255.0.0	65,536	65,531	Primary VPC Network CIDR
/20	255.255.240.0	4,096	4,091	Large Container / Kubernetes Node Pools
/24	255.255.255.0	256	251	Public Web Tier / Application Load Balancers
/26	255.255.255.192	64	59	Database Tier / Private Subnet Group
/28	255.255.255.240	16	11	Isolated Management / Bastion Tier

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