Private vs Public IP (IPv4) vs Elastic IPs

Identity within a network.

• Networking has two sorts of IPs. IPv4 and IPv6:

  • IPv4: 1.160.10.240

  • IPv6: 3ffe:1900:4545:3:200:f8ff:fe21:67cf

• IPv4 is still the most common format used online.

• IPv6 is newer and solves problems for the Internet of Things (IoT).

• IPv4 allows for 3.7 billion different addresses in the public space.

• IPv4: [0-255].[0-255].[0-255].[0-255]

Private vs Public IP (IPv4) vs Elastic IPs Fundamental Differences

Public IP:

• Public IP means the machine can be identified on the internet (WWW).

• Must be unique across the whole web (not two machines can have the same public IP).

• Can be geo-located easily.

Private IP:

• Private IP means the machine can only be identified on a private network only

• The IP must be unique across the private network.

• BUT two different private networks (two companies) can have the same IPs.

• Machines connect to WWW using a NAT + internet gateway (a proxy)

• Only a specified range of IPs can be used as private IP.

Elastic IPs:

• When you stop and then start an EC2 instance, it can change its public IP.

• If you need to have a fixed public IP for your instance, you need an Elastic IP

• An Elastic IP is a public IPv4 IP you own as long as you don’t delete it.

• You can attach it to one instance at a time.

• With an Elastic IP address, you can mask the failure of an instance or software by rapidly remapping the address to another instance in your account.

• You can only have 5 Elastic IP in your account (you can ask AWS to increase that).

• Overall, try to avoid using Elastic IP:

  • They often reflect poor architectural decisions.

  • Instead, use a random public IP and register a DNS name to it.

  • Or, as we’ll see later, use a Load Balancer and don’t use a public IP.

IP's In AWS EC2

If your machine is stopped and then started, the public IP can change.

• By default, your EC2 machine comes with:

  • A private IP for the internal AWS Network

  • A public IP, for the WWW.

  When we are doing SSH into our EC2 machines:

  • We can’t use a private IP, because we are not in the same network.

  • We can only use the public IP.