Blog ENG - Cisco - Post 1 2025
In the world of networking, clear and unambiguous documentation is crucial. To aid in this, the Internet Engineering Task Force (IETF) has reserved specific IPv4 address blocks for use in examples and documentation. This initiative is encapsulated in RFC 5737, a document that outlines the purpose and use of these reserved address blocks.
What is RFC 5737?
RFC 5737, titled “IPv4 Address Blocks Reserved for Documentation,” was published in January 2010. It describes three IPv4 unicast address blocks that are reserved exclusively for use in documentation and specifications. These blocks are:
- 192.0.2.0/24 (TEST-NET-1)
- 198.51.100.0/24 (TEST-NET-2)
- 203.0.113.0/24 (TEST-NET-3)
The primary goal of reserving these blocks is to prevent conflicts and confusion that could arise from using real, assigned IP addresses in examples. By using these designated ranges, authors can ensure that their documentation is clear and that the addresses used will not interfere with actual network operations.
Why Are These Blocks Important?
Using real IP addresses in documentation can lead to unintended consequences, such as network conflicts or security issues. The reserved blocks provided by RFC 5737 offer a safe alternative, ensuring that the examples remain hypothetical and do not impact real-world networks.
These blocks are particularly useful for:
- Educational Materials: Instructors and authors can use these addresses in textbooks, tutorials, and training materials without worrying about causing network issues.
- Technical Documentation: Engineers and developers can include these addresses in technical specifications, whitepapers, and manuals to illustrate concepts and configurations.
- Software Development: Developers can use these addresses in code examples, ensuring that their documentation is both accurate and safe.
Operational Implications
RFC 5737 specifies that addresses within the TEST-NET-1, TEST-NET-2, and TEST-NET-3 blocks should not appear on the public Internet. Network operators are advised to add these address blocks to their list of non-routable address spaces and include them in packet filters if deployed. This ensures that these addresses remain confined to documentation and do not accidentally get used in live networks.
Conclusion
RFC 5737 plays a vital role in maintaining the clarity and safety of network documentation. By reserving specific IPv4 address blocks for use in examples, the IETF has provided a valuable tool for educators, developers, and network engineers. Whether you’re writing a technical manual or developing a new software application, using these reserved blocks can help you create clear, conflict-free documentation.