Reserved and Future-Use IPv4 Address Space
Overview
Not all IPv4 ranges are assignable—even if they aren’t private or multicast. Several blocks are reserved for future use, experiments, or system-level operations.
These ranges are often misunderstood and sometimes misused in lab environments. Misuse can lead to routing instability, broadcast storms, or conflicts with system behaviors.
What This CSV Contains
Key reserved ranges include:
- 0.0.0.0/8 — Special-purpose, including 0.0.0.0/32 for default route
- 240.0.0.0/4 — Reserved “Class E” space
- 255.0.0.0/8 — Reserved + broadcast context
Each entry includes:
- CIDR block
- Description
- Summary
- Detailed notes on behavior and best practices
This page helps readers understand why these ranges are “off limits” for normal networking.
| CIDR | Name | Summary | Notes |
|---|---|---|---|
| 0.0.0.0/8 | This Network / Partly Reserved | Contains special addresses including 0.0.0.0/32; not used for standard host assignments. | Used in bootstrapping, default routes, and special signaling; never assigned to ordinary hosts. |
| 240.0.0.0/4 | Reserved for Future Use | Entire block reserved/experimental. | Historically treated as unusable; some modern stacks can technically route it, but it remains reserved and non-routable on the public Internet. |
| 255.0.0.0/8 | Reserved / Broadcast Context | Top-end reserved / broadcast-related space. | 255.255.255.255/32 is limited broadcast; the rest of 255/8 is reserved and not assignable. |