1.7 Given a scenario, use appropriate IPv4 network addressing
Address Types
📘CompTIA Network+ (N10-009)
1. What is RFC1918?
RFC1918 is a standard defined by the Internet Engineering Task Force (IETF) that specifies private IPv4 addresses.
- Private IP addresses are addresses that are not routable on the public internet.
- These addresses are used inside organizations, like in offices, schools, or data centers, to create internal networks.
Think of them as “internal addresses” that only work within your own network. Devices with RFC1918 addresses cannot communicate directly with the public internet without a process called NAT (Network Address Translation).
2. Why is RFC1918 Important?
- Conserves public IP addresses: The IPv4 address space is limited, so using private addresses internally reduces the need for public IPs.
- Enhances security: Devices with private addresses are not directly reachable from the internet.
- Simplifies internal network management: Organizations can assign IPs internally without coordinating with a central authority.
3. The RFC1918 Private IP Ranges
RFC1918 defines three main IPv4 ranges for private networks:
| Range | CIDR Notation | Subnet Mask | Usable IP Addresses | Common Use |
|---|---|---|---|---|
| 10.0.0.0 – 10.255.255.255 | 10.0.0.0/8 | 255.0.0.0 | 16,777,214 | Large enterprise networks |
| 172.16.0.0 – 172.31.255.255 | 172.16.0.0/12 | 255.240.0.0 | 1,048,574 | Medium-sized networks |
| 192.168.0.0 – 192.168.255.255 | 192.168.0.0/16 | 255.255.0.0 | 65,534 | Small networks / home networks |
Key Notes:
- CIDR notation (like /8, /12, /16) tells you how many bits are used for the network portion of the address.
- These ranges are reserved only for internal use. You cannot use them on the public internet.
4. How RFC1918 Addresses Work in IT Environments
a. Internal Network Communication
- Devices like computers, printers, servers, and VoIP phones in an organization can all communicate using private IPs.
- Example: A file server at
192.168.1.10can communicate with a workstation at192.168.1.20internally.
b. Accessing the Internet
- To connect to the internet, private IPs use NAT (Network Address Translation) on a router or firewall.
- NAT converts private IP addresses to a public IP address.
- Example: A laptop with
192.168.1.15accesses a website; the router translates it to a public IP like203.0.113.10so the site can respond.
c. Segmentation and Security
- Organizations can divide private IP ranges into subnets for different departments (Finance, IT, HR).
- Firewalls can restrict traffic between subnets for security.
5. RFC1918 vs Public IPs
| Feature | RFC1918 Private IPs | Public IPs |
|---|---|---|
| Internet Reachable | No | Yes |
| Assigned by ISP | No | Yes |
| Security | Safer inside networks | Exposed to the internet |
| Cost | Free | Must be obtained from ISP |
6. Exam Tips
- Know the three private IP ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16).
- Understand that RFC1918 addresses are internal-only and require NAT for internet access.
- Remember the use cases: internal networking, security, and conserving public IPs.
- Be able to distinguish private vs public IPs in scenario-based questions.
✅ Summary in Simple Terms:
RFC1918 is the standard for private IPv4 addresses. It defines certain ranges that can be used inside networks but cannot be used directly on the internet. Devices with these addresses communicate internally and rely on NAT to reach the outside world. Knowing the ranges, purposes, and how NAT works is essential for Network+ exam questions.
