All technological notes.
AWS VPCVPC / Virtual Private Cloud
You can have multiple VPCs in an AWS region (max. 5 per region – soft limit)
Max. CIDR per VPC is 5, for each CIDR:
/28 (16 IP addresses)/16 (65536 IP addresses)Because VPC is private, only the Private IPv4 ranges are allowed:
10.0.0.0 – 10.255.255.255 (10.0.0.0/8)172.16.0.0 – 172.31.255.255 (172.16.0.0/12)192.168.0.0 – 192.168.255.255 (192.168.0.0/16)Your VPC CIDR should NOT overlap with your other networks (e.g., corporate)
5 VPC / region5 CIDR / VPC/16 - /28 / CIDR




Default VPC Walkthrough172.16.0.0/12default VPCEC2 instances are launched into the default VPC if no subnet is specifiedDefault VPC
EC2 instances inside it have public IPv4 addressesIPv4 DNS names173.16.0.0/12


AWS reserves 5 IP addresses (first 4 & last 1) in each subnet
e.g.: if CIDR block 10.0.0.0/24, then reserved IP addresses are:
Network AddressVPC routerAmazon-provided DNSNetwork Broadcast Address. AWS does not support broadcast in a VPC, therefore the address is reservedExam Tip, if you need 29 IP addresses for EC2 instances:









Note:
By default, Auto-assign IP settings is disable.
