Elastic IP / IP addresses

Question 1

Public IPv4

Answer 1

• machine can be identified on the internet
• must be unique across the whole web
• easily geolocated

Question 2

Private IPv4

Answer 2

• machine identified on public network only
• unique across network only
• machines connect to the internet using a NAT device + internet gateway (a proxy)
• only specified range (RFC 1918):
  
  • Class A:10.0.0.0to10.255.255.255
  • Class B:172.16.0.0to172.31.255.255
  • Class C:192.168.0.0to192.168.255.255

Question 3

Elastic IP (try to avoid using)

Answer 3

• Fixed public IP for an EC2 instance (even if starting and stopping)
• own it as long as you delete it
• attach to one instance at a time
• default maximum 5 elastic IP addresses in an account (can request more)
• BETTER ALTERNATIVE - use a random public IP and register a DNS name to it, or a load balancer