RFC 5737 / START HERE
IPv4 example addresses, before the details
IPv4 Address Blocks Reserved for Documentation. TEST-NET is a label for example networks, not a new network protocol.
Internet Protocol version 4 (IPv4) uses four dotted numbers to label network interfaces. This RFC reserves three address ranges for written examples, so a tutorial can show several different networks.
Why it exists
Picking an arbitrary address can accidentally refer to someone else’s network. RFC 5737 adds two documentation ranges beside the older 192.0.2.0/24 block and explains their operational limits. It is Informational guidance, not a packet transport specification.
A familiar example
A tutorial can give its fictional client 192.0.2.7 and fictional server 198.51.100.9. These are labels on the page, not services to contact or addresses to copy into a real lab. The chapters show the three ranges, prefix boundaries, filtering guidance, local-use limits, and a historical trap.
Helpful background
You can start here without reading another RFC. If these ideas are unfamiliar, these short introductions may help.
What you’ll learn next
Begin with chapter one, or choose a topic.
- Give each example network its own rangeThree reserved IPv4 blocks let a document distinguish separate networks without borrowing someone else’s addresses.→
- Read what the /24 boundary includesAn IPv4 address has 32 bits. A /24 prefix fixes the first 24 bits: the first three eight-bit numbers in dotted-decimal notation.→
- Keep example addresses off the public InternetA reservation describes how addresses should be used. Operators still need an actual routing or filtering policy.→
- Separate documentation from private deploymentA diagram on paper and a running local network are different uses. RFC 5737 explicitly says its blocks are not for local use.→
- Replace a misleading historical example128.66.0.0/16 appeared in older examples, but RFC 5737 explains that this did not reserve it.→
This introduction explains RFC 5737 (2010). Read the original RFC ↗