1. Private IPv4 Addressing

Private IPv4 addresses are a range of IP addresses not routable on the public internet. They are primarily used within local networks and are defined by the Internet Engineering Task Force (IETF) in RFC 1918. These addresses allow devices within the same network to communicate with each other without needing a public IP address, conserving the limited IPv4 address space.

1.1 The Need for Private IP Addresses

The exhaustion of the IPv4 address space necessitated a method to use IP addresses within internal networks without consuming the limited public address space. Private IP addresses serve this purpose, allowing organizations to use the same IP ranges without conflict, as these addresses are isolated to internal networks.

1.2 Private IPv4 Address Ranges

The IETF has designated three blocks of IP addresses as private. These ranges are:

• 10.0.0.0/8: This range allows for 16,777,216 addresses and is often used in large organizations.
• 172.16.0.0/12: This range provides 1,048,576 addresses and is commonly used by medium-sized networks.
• 192.168.0.0/16: This range offers 65,536 addresses and is typically used in home networks and small businesses.

1.3 Characteristics of Private IPv4 Addresses

Private IP addresses have distinct characteristics that differentiate them from public IP addresses:

• Non-Routable on the Internet: Devices with private IP addresses cannot directly access the internet. They require Network Address Translation (NAT) to communicate with external networks.
• Reusability: Multiple organizations can use the same private IP address ranges within their internal networks without conflict, as these networks are isolated.
• Security: Private IP addresses add a layer of security by isolating the internal network from external networks.

1.4 Network Address Translation (NAT)

Since private IP addresses cannot directly access the internet, NAT is used to map private IP addresses to a public IP address when communicating with external networks. NAT operates at the router level and translates the private IP addresses of devices within a local network to a single public IP address or a pool of public IP addresses.

1.4.1 NAT Working Principle

When a device with a private IP address initiates a connection to the internet, NAT changes the source address of the outgoing packet to a public IP address. When the response comes back, NAT translates the destination address back to the original private IP address, ensuring that the packet reaches the correct device within the local network.

Private IP (192.168.1.5) -> NAT -> Public IP (203.0.113.5)

1.5 Advantages of Private IPv4 Addressing

The use of private IP addresses offers several advantages:

• IP Address Conservation: Private IP addressing helps conserve the global IPv4 address space by allowing the reuse of the same IP ranges in different networks.
• Enhanced Security: Private IP addresses keep internal network traffic isolated, making it more difficult for external threats to penetrate the network.
• Flexibility: Organizations can freely assign and manage IP addresses within their private networks without needing to coordinate with external entities.