Explain IP Address and RFC 1918

1. What is an IP Address?

An IP (Internet Protocol) address is a unique address assigned to a device on a network. It helps devices identify each other and communicate with one another.

Think of an IP address like a house address.

For example:

• Computer A → 192.168.1.10
• Computer B → 192.168.1.20

When Computer A wants to communicate with Computer B, the IP address helps the network know where to send the data.

2. What is RFC 1918?

In 1996, IETF published RFC 1918, which reserved specific IPv4 address ranges for private networks. These addresses are used inside organizations, homes, and cloud networks and cannot be directly routed on the public Internet.

Private IP Ranges

There are three reserved ranges:

• 10.0.0.0/8 → 10.0.0.0 – 10.255.255.255 → Large networks
• 172.16.0.0/12 → 172.16.0.0 – 172.31.255.255 → Medium networks
• 192.168.0.0/16 → 192.168.0.0 – 192.168.255.255 → Small/home networks

Network and Broadcast Address

Every subnet has two special addresses:

• Network Address → First address of the subnet
• Broadcast Address → Last address of the subnet

The addresses between them can normally be assigned to devices.

How RFC 1918 Works with NAT

Private IP addresses cannot communicate directly with the public Internet, so NAT (Network Address Translation) is commonly used.

Device --- Router --- NAT --- Public IP --- Internet 192.168.1.10

Process:

• Our device sends a request using its private IP.
• The router receives the request.
• NAT changes the private IP to the router's public IP.
• The router sends the request to the Internet.
• The response returns to the router.
• The router uses NAT to send the response back to our private device.