• AWS supports both types of IP’s
  • IPv4 e.g. 1.160.10.240
    • Allows 3.7 billion addresses that’s almost running out today.
      • [0-255].[0-255].[0-255].[0-255]
  • IPv6 e.g. 3ffe:1900:4545:3:200:f8ff:fe21:67cf
    • Newer & commonly used for IoT (internet of things) as it solves a lot of problems.
    • 💡 IPv6 are all public addresses (global unicast addresses)
• 💡❗ Use private IP whenever possible: Communication using Public, Elastic IP or Elastic Load Balancer inside EC2 network costs Data Transfer changes even in same AZ.
• Bring Your Own IP Addresses (BYOIP)
  • You can bring part or all of your public IPv4 address range from your on-premises network to your AWS account
  • You need to create a ROA (Route Origin Authorization)
    • A document that you can create that contains the address range, the ASNs that are allowed to advertise the address range, and an expiration date.

CIDR (IPv4)

• Classless Inter-Domain Routing
• Used for Security Groups rules, or AWS networking in general
• ❗ Max CIDR size in AWS is /16
• CIDR has two components:
  • The base IP (XX.XX.XX.XX)
    • The base IP represents an IP contained in the range
  • The subnet mask (/26)
    • Defines how many bits can change in the IP
    • Can take two forms:
      1. 255.255.255.0: Less common
      2. /24: More common

    • Basically allows part of the underlying IP to get additional values from the base IP

      Range	Total Allowed IPs	Calculation
      /32	1 IP	2 ^ 0
      /31	2 IP	2 ^ 1
      /30	4 IP	2 ^ 2
      /29	8 IP	2 ^ 3
      /28	16 IP	2 ^ 4
      /27	32 IP	2 ^ 5
      /26	64 IP	2 ^ 6
      /25	128 IP	2 ^ 7
      /24	256 IP	2 ^ 8
      /16	65.536 IP	2 ^ 16
      /0	all IPs	2 ^ 32

    • 📝 So just know that 32 - CIDR number = X power of 2
      • E.g 192.168.0.0/24:
        • 32 - 24 = 8 => 2 ^ 8 = 256 IP addresses
        • Between 192.168.0.0 - 192.168.0.255 (256 IP)
        • Decimal subnet mask = 255.255.255.0
      • E.g. 192.168.0.0/16:
        • 32 - 16 = 16 => 2 ^ 16 = 65.536 IP addresses
        • Between 192.168.0.0 - 192.168.255.255
        • Decimal subnet mask = 255.255.0.0
    • 💡📝 Memo
      • Each 8 points from 32 represents which IP number can change totally:
        • /32 - no IP number can change
        • /24 - last IP number can change
        • /16 - last IP two numbers can change
        • /8 - last IP three numbers can change
        • /0 - all IP numbers can change

Public & Private IP

• Private vs Public IP (IPv4)
  • IANA had defined blocks of IPv4 addresses for private (LAN) and public (Internet) access
    • IANA: The Internet Assigned Numbers Authority
  • Public IP
    • Machine can be identified on internet (WWW)
    • Must be unique across the whole web (two machines cannot have same public IP)
    • Can be geo-located easily
  • Private IP
    • Machine can only be identified on a private network only
    • IP must be unique across the private network.
    • Machines connect to WWW using an internet gateway (a proxy)
    • Only a specified range of IPs can be used as private IP
      • 10.0.0.0 - 10.255.255.255 (10.0.0.0/8) <- in big networks
      • 172.16.0.0 - 172.1.255.255 (172.16.0.0/12) <- default AWS one
      • 192.168.0.0 - 192.168.255.255 (192.168.0.0/16) <- e.g. home networks
    • AWS registers 5 IP addresses per subnet, see VPC - Subnets for more information.
  • Other reserved ranges
    • 🤗Trivia ^{StackOverflow}
      • 169.254.0.0/16 exists only on the directly connected network.
      • It’s a reserved IPv4 Link Local Address.
      • AWS choose its metadata server to make it reachable within this range (169.254.169.254).
    • 127.0.0.0 – 127.255.255.255 is used for addresses to the local host.
• Elastic IP
  • Fixed public IPv4 IP address for attaching to EC2 instances (to their Elastic Network Interfaces).
    • Because when you stop & start an EC2 instance, it’ll change its public IP.
  • You own it as long as you don’t delete it.
  • Can help you mask the failure of an instance by remapping the address to another instance.
  • You can attach it to a one instance at a time
  • ❗ Max 5 Elastic IP per account (soft limit)
  • 💡 Elastic IP reflects often poor architectural decisions
    • Horizontal scaling becomes much harder
    • Instead you can:
      • Use a random public IP and register a DNS name to it.
      • Load balancer (best pattern).
  • Pricing
    • Elastic IPs are free as long as
      • They are being used by an instance i.e. attached to instance and instance is running.
        • ❗ Amazon will charge you $0.01 per hour for each EIP that you reserve and do not use.
      • The instance has only one Elastic IP address attached to it.
    • ❗ You will be charged if you ever remap an EIP more than 100 times in a month.

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