Allocated but unannounced space
Every block here was allocated or assigned by a regional internet registry, and none of them appeared in any routing table we collected at our last snapshot — neither as a route of their own, nor covered by a larger announcement, nor carved up into more specifics.
“Unannounced” does not mean “unused”
Plenty of allocated space is deliberately kept off the public internet: private interconnects, lab and lawful-intercept ranges, networks reachable only inside one operator, and space held in reserve. Some of it is announced somewhere our collectors cannot see, which is a limit of our vantage points rather than a fact about the block.
It is also a snapshot, not a history: a block announced yesterday and withdrawn this morning appears here today. Nothing on this page means a block is unallocated, available, or free to announce.
Browse by registry
Browse by country
Countries with the most unannounced blocks, largest first.
Unannounced blocks
85,195 blocks match, ordered by prefix.
| Prefix | Addresses | Registry | Country | Allocated |
|---|---|---|---|---|
| 192.51.16.0/20 | 4.1k | APNIC |  JP | 2nd Aug 1993 |
| 192.51.160.0/21 | 2k | APNIC | JP | 7th May 1993 |
| 192.51.172.0/23 | 512 | APNIC |  CN | 24th Jul 2025 |
| 192.51.176.0/24 | 256 | APNIC | JP | 5th Aug 1993 |
| 192.51.177.0/24 | 256 | APNIC | JP | 5th Aug 1993 |
| 192.51.178.0/24 | 256 | APNIC | JP | 5th Aug 1993 |
| 192.51.179.0/24 | 256 | APNIC | JP | 5th Aug 1993 |
| 192.51.180.0/22 | 1k | APNIC | JP | 5th Aug 1993 |
| 192.51.184.0/24 | 256 | APNIC | JP | 5th Aug 1993 |
| 192.51.185.0/24 | 256 | APNIC | JP | 5th Aug 1993 |
| 192.51.186.0/24 | 256 | APNIC | JP | 5th Aug 1993 |
| 192.51.187.0/24 | 256 | APNIC | JP | 5th Aug 1993 |
| 192.51.189.0/24 | 256 | APNIC | JP | 5th Aug 1993 |
| 192.51.190.0/23 | 512 | APNIC | JP | 5th Aug 1993 |
| 192.51.196.0/22 | 1k | APNIC | JP | 21st Feb 1989 |
| 192.51.200.0/21 | 2k | APNIC | JP | 6th Aug 1993 |
| 192.51.225.0/24 | 256 | APNIC | JP | 6th Aug 1993 |
| 192.51.226.0/24 | 256 | APNIC | JP | 6th Aug 1993 |
| 192.51.227.0/24 | 256 | APNIC | JP | 6th Aug 1993 |
| 192.51.228.0/24 | 256 | APNIC | JP | 6th Aug 1993 |
| 192.51.229.0/24 | 256 | APNIC | JP | 6th Aug 1993 |
| 192.51.230.0/24 | 256 | APNIC | JP | 6th Aug 1993 |
| 192.51.231.0/24 | 256 | APNIC | JP | 6th Aug 1993 |
| 192.51.232.0/24 | 256 | APNIC | JP | 6th Aug 1993 |
| 192.51.233.0/24 | 256 | APNIC | JP | 21st Feb 1989 |
| 192.51.234.0/24 | 256 | APNIC | JP | 6th Aug 1993 |
| 192.51.235.0/24 | 256 | APNIC | JP | 6th Aug 1993 |
| 192.51.236.0/24 | 256 | APNIC | JP | 6th Aug 1993 |
| 192.51.237.0/24 | 256 | APNIC | JP | 6th Aug 1993 |
| 192.51.238.0/24 | 256 | APNIC | JP | 6th Aug 1993 |
| 192.51.239.0/24 | 256 | APNIC | JP | 6th Aug 1993 |
| 192.51.241.0/24 | 256 | APNIC | JP | 6th Aug 1993 |
| 192.51.242.0/24 | 256 | APNIC | JP | 6th Aug 1993 |
| 192.51.243.0/24 | 256 | APNIC | JP | 6th Aug 1993 |
| 192.51.244.0/24 | 256 | APNIC | JP | 6th Aug 1993 |
| 192.51.245.0/24 | 256 | APNIC | JP | 6th Aug 1993 |
| 192.51.246.0/24 | 256 | APNIC | JP | 6th Aug 1993 |
| 192.51.247.0/24 | 256 | APNIC | JP | 6th Aug 1993 |
| 192.51.248.0/24 | 256 | APNIC | JP | 6th Aug 1993 |
| 192.51.249.0/24 | 256 | APNIC | JP | 6th Aug 1993 |
| 192.51.250.0/24 | 256 | APNIC | JP | 7th May 1993 |
| 192.51.251.0/24 | 256 | APNIC | JP | 7th May 1993 |
| 192.51.253.0/24 | 256 | APNIC | JP | 6th Aug 1993 |
| 192.51.254.0/24 | 256 | APNIC |  NZ | 24th Jul 2025 |
| 192.51.255.0/24 | 256 | APNIC | JP | 21st Feb 1989 |
| 192.51.32.0/22 | 1k | APNIC | JP | 2nd Aug 1993 |
| 192.51.36.0/24 | 256 | APNIC | JP | 2nd Aug 1993 |
| 192.51.37.0/24 | 256 | APNIC | JP | 21st Feb 1989 |
| 192.51.38.0/24 | 256 | APNIC | JP | 21st Feb 1989 |
| 192.51.44.0/24 | 256 | APNIC | JP | 2nd Aug 1993 |