section 6

• Private IP


  IP address used within a private network, can be reused across different private networks
• Public IP


  IP address accessible over the internet, must be unique globally
• IPv4 is the most common IP version, has 4 numbers separated by dots
• IPv6 is less common, has a long string of exotic symbols, numbers and letters
• This course will focus on IPv4
• IPv4 allows for 3.7 billion different addresses, which is almost running out
• Each IPv4 number can vary between 0 and 255
• Private network


  Computers within the network can talk to each other using private IPs
• Computers in private network


  Can talk to each other using private IPs
• Computers in private network

  Access internet through internet gateway and public IP
• Different companies can have the same private IP range
• Public IP


  • Machine can be identified on the internet
  • Must be unique globally
• Private IP


  • Machine can only be identified on the private network
  • Must be unique only within the private network
• Machines on private network connect to internet through NAT device and internet gateway
• Only specified IP ranges can be used as private IPs
• Elastic IP


  • Public IPv4 address that you own and can attach to one instance at a time
  • Can be used to mask instance or software failures by quickly moving it to another instance
• Elastic IPs are often considered an architectural anti-pattern, it's better to use random public IPs and DNS names instead
• By default, EC2 instances get a private IP for internal AWS network and a public IP for internet access
• When SSH'ing into an EC2 instance, you can only use the public IP unless you have a VPN
• The public IP of an EC2 instance can change when it is stopped and started
• Public IPv4


  IPv4 address that can be used to SSH into the instance from the public internet
• Private IP


  IP address attached to the instance that can only be accessed from within the private network
• Trying to SSH using the private IP


  Does not work because the private IP is only accessible within the private network
• Stopping and starting an instance

  Public IPv4 address changes, private IP address does not change
• Elastic IP


  An IP address that you own and can associate with an EC2 instance, which ensures the public IP address does not change when the instance is stopped and started
• Pricing for public IPv4 and elastic IPs is $0.005 per hour, around $3.50 per month
• AWS provides 750 hours per month of free public IPv4 addresses
• Associating an elastic IP with an instance

  Allocate an elastic IP

  2. Associate the elastic IP with the instance
• Instance is stopped


  Elastic IP remains attached, public IPv4 does not change
• Disassociating and releasing an elastic IP


  Disassociate the elastic IP from the instance

  2. Release the elastic IP to stop being billed for it
• Elastic Network Interfaces (ENI)


  Logical component in a VPC that represents a virtual network card
• ENI


  • Gives EC2 Instances access to the network
  • Used outside EC2 Instances as well
• ENI attributes


  1. Primary private IPv4

  2. One or more secondary IPv4

  3. Elastic IPv4 per private IPv4

  4. One or more public IPv4

  5. One or more security groups

  6. MAC address
• ENIs are bounded to a specific availability zone (AZ)
• Moving ENI between EC2 instances

  1. Move ENI from first EC2 instance to second EC2 instance

  2. Changes the private IP from first instance to second instance

  3. Helpful for failovers when EC2 instance accessed by private static IP
• Launching two instances


  1. Scroll down

  2. Choose Amazon Linux 2, t.2.micro

  3. Choose key pair

  4. Use existing security group

  5. Launch instances
• Network interfaces


  • Each instance has one network interface
  • Each interface contains a public IPv4, a private IPv4 and a private IPv4 DNS
• Creating a new network interface

  1. Give description

  2. Select subnet

  3. Auto assign private IPv4

  4. Attach security group

  5. Create network interface
• Creating a new network interface


  Provides a secondary private IPv4
• Attaching the new network interface to an instance


  1. Choose instance to attach to

  2. Attach network interface