Read what the /24 boundary includes
02An IPv4 address has 32 bits. A /24 prefix fixes the first 24 bits: the first three eight-bit numbers in dotted-decimal notation.
192.0.3.7 changes the third number, so it is outside TEST-NET-1 and outside the other two documentation blocks.
Source for this drawing: RFC 5737 · Read RFC section 3 ↗
New to this? Start hereA quick picture + helpful background
A message needs an address.
Think of a packet as a small addressed envelope. Devices pass it onward; transport protocols decide what delivery promises an application gets.
Helpful first, if these ideas are unfamiliar
These pictures are analogies to help you learn. The linked RFC explains the actual rules.
Terms in this drawing
Related RFCs and changes
“Updates” changes part of an earlier RFC. “Obsoletes” replaces it. This list shows selected related documents.
Match the prefix, not just a familiar-looking part of the address.
- Each listed block has 256 address values, from last number 0 through 255.
- 192.0.2.7 is inside TEST-NET-1; 192.0.3.7 is outside all three blocks.
- This membership example does not say that all 256 values are assignable host addresses on a deployed subnet. CIDR prefix notation is explained in RFC 4632 §3.1.
Examples are documentation text, not a network configuration. No packets are sent. SHOULD and SHOULD NOT are recommendations, not MUST. Valid exceptions require understanding and carefully weighing the full implications (RFC 2119 §§3–4).
Read the RFC section ↗