Subnet

• Subnets are tied to specific AZ
• Multiple Subnets can be provisioned in one AZ
• One Subnet can not be provisioned in multi-AZ
• Two types of Subnets
• Public Subnet use to put Load balancer
• Private Subnet use to put Applications and DB Servers
• Every time create a Subnet, loose 5 IP address.
• First 4 and the last one
• First one for Network Address
• Second one for VPC Router, reserved by AWS
• Third one for AWS Provided DNS, reserved by AWS
• Fourth one for future use, reserved by AWS
• Last one for Broadcast Address, although AWS does not support Broadcast
• Exercise
• Can /27 handle 29 IP Address?
  • It has 2^(32-27) = 32 IP Address
  • Since 5 IP address is not usable, we can use 32-5 = 27 IP Address
  • So /27 can not handle more than 27 IP Address
  • To handle 29 IP Address we might need at least /26 i.e. 2^(32-26) = 64 IP Address
  • In this case we can use 64-5 = 59 IP Address, that matches the requirements
• We can enable Auto Assign Public IPv4 Address features, so any instance being created within the subnet, will have a public IP.
• In Custom VPC, the feature Auto Assign Public IPv4 Address is disabled by default, whereas in Default VPC it is enabled by default.
• To ensure the Public Subnet can access the Private Subnet, need to ensure, the SG have the required rules defined to allow traffic
• Since internet and intranet is corresponding to separate AZ, need separate AZ for them