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VPC Basics

Introduction

  • No of IP Addresses in a VPC = 2(32-CIDR Range) e.g a /28 CIDR will have 2(32-28) = 24=16 IP Addresses
  • VPC are regional services, are regionally resilient & operate within multiple AZ in a region
  • VPC is by default Private & Isolated.
  • An Account can have 1 default VPC & multiple custom VPCs
  • An account gets 1 default VPC per region
  • VPC CIDR defines start & end IP for a VPC
  • Each VPC is subdivided in subnets. Each subnet is located in one AZ. This is set on creation & can not be changed later
  • Tenancy can be set to default or Dedicated at VPC level. If it is set to Dedicated for a VPC, all the EC2s in the VPC get Dedicated Tenants which has a cost implication.
  • A VPC with Default tenancy can have EC2s with dedicated tenancy on per instance basis
  • A VPC has 1 primary Private IPV4 CIDR block by defailt. It can additionally have upto 5 secondary IPV4 blocks
  • The VPC CIDR range can be between Min /28 (i.e. 16 IP) to Max/16(i.e. 65,536 IP)
  • Optionally a single IPV6/56 CIDR block can be assigned

Default VPC

  • Always has the same CIDR 172.31.0.0/16
  • Has one subnet in every availability zone. Each subnet has a /20 CIDR
  • Default VPC can be deleted and recreated
  • Some services assume presume presence of default VPC
  • It is provided with Internet Gateway, Security Group & NACL automatically
  • Anything placed in default VPC is automatically assigned a public IPV4 address

VPC Sizing

  • VPCs can be minimum /28(16 IPs) & maximum /16(65536 IPs)

DNS in VPC

  • Have fully featured DNS provided by Route53
  • Available on base IP address + 2
  • enableDnsHostnames - gives instances with public ip addresses get public DNS name
  • enableDnsSupport - DNS resolution is enabled or disabled within a VPC