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VPC In AWS, What is VPC (Virtual Private Cloud)?, Describe CIDR Blocks,…

- - - - You cannot detach a primary network interface from an instance
      - You can create and attach an additional network interface to any instance in your VPC
      - The number of network interfaces you can attach varies by instance type
- - - - Modifying the public IP addressing attribute of your subnet
      - Enabling or disabling the public IP addressing feature during instance launch, which overrides the subnet's public IP addressing attribute
    - - We resolve a public DNS hostname to the public IP address of the instance outside the instance network
      - the private IP address of the instance from within the instance network
  - - - You manually assign an IPv6 address to your instance during launch.
      - You assign an IPv6 address to your instance after launch.
      - Your subnet is configured to automatically assign an IPv6 address to the primary network interface of an instance during launch.
      - You assign an IPv6 address to a network interface in the same subnet, and attach the network interface to your instance after launch.
    - - You can disassociate the IPv6 address from the primary network interface
      - We do not support IPv6 DNS hostnames for your instance
    - - You cannot reassign an IPv6 address while it's assigned to another network interface you must first unassign it.
    - - The number of IPv6 addresses you can assign to a network interface, and the number of network interfaces you can attach to an instance varies per instance type
    - - You can control whether instances are reachable via their IPv6 addresses by controlling the routing for your subnet
      - using security group and network ACL rules
- - - - When creating a VPC, you must specify an IPv4 CIDR block for the VPC
      - The allowed block size is between a /16 netmask (65,536 IP addresses) and /28 netmask (16 IP addresses)
      - After you've created your VPC, you can associate secondary CIDR blocks with the VPC
      - The CIDR block of a subnet can be the same as the CIDR block for the VPC (for a single subnet in the VPC), or a subset of the CIDR block for the VPC (for multiple subnets).
        
        The allowed block size is between a /28 netmask and /16 netmask. If you create more than one subnet in a VPC, the CIDR blocks of the subnets cannot overlap.
        
        example: VPC with CIDR block 10.0.0.0/24, it supports 256 IP addresses.
        
        You can break this CIDR block into two subnets, each supporting 128 IP addresses.
        
        One subnet uses CIDR block 10.0.0.0/25 (for addresses 10.0.0.0 - 10.0.0.127)
        
        the other uses CIDR block 10.0.0.128/25 (for addresses 10.0.0.128 - 10.0.0.255).
        
        tools available on the internet to help you calculate and create IPv4 subnet CIDR blocks; for example, IPv4 Address Planner
        
        first four IP addresses and the last IP address in each subnet CIDR block are not available for you to use, and cannot be assigned to an instance
        
        example: subnet with CIDR block 10.0.0.0/24, the following five IP addresses are reserved
        
        10.0.0.2: Reserved by AWS. The IP address of the DNS server is the base of the VPC network range plus two
        
        10.0.0.3: Reserved by AWS for future use.
        
        10.0.0.1: Reserved by AWS for the VPC router.
        
        10.0.0.255: Network broadcast address. We do not support broadcast in a VPC, therefore we reserve this address.
        
        10.0.0.0: Network address.
        
        Adding IPv4 CIDR blocks to a VPC
        
        The allowed block size is between a /28 netmask and /16 netmask.
        
        There are restrictions on the ranges of IPv4 addresses you can use
        
        The CIDR block must not overlap with any existing CIDR block that's associated with the VPC.
        
        You cannot increase or decrease the size of an existing CIDR block.
        
        You have a quota on the number of CIDR blocks you can associate with a VPC and the number of routes you can add to a route table. You cannot associate a CIDR block if this results in you exceeding your quotas
    - - You can associate a single IPv6 CIDR block with an existing VPC in your account, or when you create a new VPC
      - The CIDR block is a fixed prefix length of /56. You can request an IPv6 CIDR block from Amazon's pool of IPv6 addresses.
      - If you've associated an IPv6 CIDR block with your VPC, you can associate an IPv6 CIDR block with an existing subnet in your VPC, or when you create a new subnet
      - example, you create a VPC and specify that you want to associate an Amazon-provided IPv6 CIDR block with the VPC
        
        2001:db8:1234:1a00::/56. You cannot choose the range of IP addresses yourself
        
        You can create a subnet and associate an IPv6 CIDR block from this range; for example, 2001:db8:1234:1a00::/64.
      - The tools available on the internet to help you calculate and create IPv6 subnet CIDR blocks; for example, IPv6 Address Planner
      - The first four IPv6 addresses and the last IPv6 address in each subnet CIDR block are not available for you to use, and cannot be assigned to an instance.
        
        example, in a subnet with CIDR block 2001:db8:1234:1a00/64,
        
        2001:db8:1234:1a00::
        
        2001:db8:1234:1a00::1
        
        2001:db8:1234:1a00::2
        
        2001:db8:1234:1a00:ffff:ffff:ffff:ffff
        
        2001:db8:1234:1a00::3
    - - Because can optionally associate an IPv6 CIDR block with your VPC.