AWS VPC Subnet Reserved Address (and ELBs)


This post is part of my note taking while studying for the AWS Certified Advanced Networking - Specialty certification.

Here are some good things to know on AWS subnet addressing.

Reserved Addresses

AWS VPC subnets reserve ‘5’ IPs by default. Why the quotes? It counts the network address and broadcast address:

Subnet Size Limits

You can assign a subnet between a /28 and /16, or between 16 and 65,536 IPs, or between 11 and 63,531 usable.

Elastic Load Balancers

The minimum subnet size for a subnet used with ELB is a /27 with 8 free IPs. You need at least two subnets in different availability zones.