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CIDR Range

81.91.80.0/21

2.0K IPs /21 Web4U s.r.o. AS39790 Czechia RIPE
Addresses
2,048
2.0K
IP Range
81.91.80.0
→ 81.91.87.255
Sub-ranges
12+
within this block
PTR Density
100.0%
2.0K of 2.0K IPs have PTR

Reputation · trust score

A transparent 0–100 signal. Every entity starts at a neutral baseline of 65; threat-intel blocklists, exposure, reverse-DNS, routing and allocation each adjust it up or down. Higher is more trustworthy.

76/100
Moderate
How this score is built

Experimental · trust-vectors model v1.2.1 — a transparent heuristic, not a definitive verdict. How it works →

Ranges inside 81.91.80.0/21

CIDRIPsOrganizationASNCountry
81.91.84.0/22 1.0K Web4U s.r.o. AS39790 CZ
81.91.82.0/23 512 Web4U s.r.o. AS39790 CZ
81.91.80.0/24 256 Web4U s.r.o. AS39790 CZ
81.91.81.128/25 128 Web4U s.r.o. AS39790 CZ
81.91.81.64/26 64 Web4U s.r.o. AS39790 CZ
81.91.81.32/27 32 Web4U s.r.o. AS39790 CZ
81.91.81.16/28 16 Web4U s.r.o. AS39790 CZ
81.91.81.0/29 8 Web4U s.r.o. AS39790 CZ
81.91.81.12/30 4 Web4U s.r.o. AS39790 CZ
81.91.81.8/31 2 Web4U s.r.o. AS39790 CZ
81.91.81.10/32 1 Web4U s.r.o. AS39790 CZ
81.91.81.11/32 1 Web4U s.r.o. AS39790 CZ

First 256 of 2,048 IP addresses in 81.91.80.0/21

81.91.80.0 81.91.80.1 81.91.80.2 81.91.80.3 81.91.80.4 81.91.80.5 81.91.80.6 81.91.80.7 81.91.80.8 81.91.80.9 81.91.80.10 81.91.80.11 81.91.80.12 81.91.80.13 81.91.80.14 81.91.80.15 81.91.80.16 81.91.80.17 81.91.80.18 81.91.80.19 81.91.80.20 81.91.80.21 81.91.80.22 81.91.80.23 81.91.80.24 81.91.80.25 81.91.80.26 81.91.80.27 81.91.80.28 81.91.80.29 81.91.80.30 81.91.80.31 81.91.80.32 81.91.80.33 81.91.80.34 81.91.80.35 81.91.80.36 81.91.80.37 81.91.80.38 81.91.80.39 81.91.80.40 81.91.80.41 81.91.80.42 81.91.80.43 81.91.80.44 81.91.80.45 81.91.80.46 81.91.80.47 81.91.80.48 81.91.80.49 81.91.80.50 81.91.80.51 81.91.80.52 81.91.80.53 81.91.80.54 81.91.80.55 81.91.80.56 81.91.80.57 81.91.80.58 81.91.80.59 81.91.80.60 81.91.80.61 81.91.80.62 81.91.80.63 81.91.80.64 81.91.80.65 81.91.80.66 81.91.80.67 81.91.80.68 81.91.80.69 81.91.80.70 81.91.80.71 81.91.80.72 81.91.80.73 81.91.80.74 81.91.80.75 81.91.80.76 81.91.80.77 81.91.80.78 81.91.80.79 81.91.80.80 81.91.80.81 81.91.80.82 81.91.80.83 81.91.80.84 81.91.80.85 81.91.80.86 81.91.80.87 81.91.80.88 81.91.80.89 81.91.80.90 81.91.80.91 81.91.80.92 81.91.80.93 81.91.80.94 81.91.80.95 81.91.80.96 81.91.80.97 81.91.80.98 81.91.80.99 81.91.80.100 81.91.80.101 81.91.80.102 81.91.80.103 81.91.80.104 81.91.80.105 81.91.80.106 81.91.80.107 81.91.80.108 81.91.80.109 81.91.80.110 81.91.80.111 81.91.80.112 81.91.80.113 81.91.80.114 81.91.80.115 81.91.80.116 81.91.80.117 81.91.80.118 81.91.80.119 81.91.80.120 81.91.80.121 81.91.80.122 81.91.80.123 81.91.80.124 81.91.80.125 81.91.80.126 81.91.80.127 81.91.80.128 81.91.80.129 81.91.80.130 81.91.80.131 81.91.80.132 81.91.80.133 81.91.80.134 81.91.80.135 81.91.80.136 81.91.80.137 81.91.80.138 81.91.80.139 81.91.80.140 81.91.80.141 81.91.80.142 81.91.80.143 81.91.80.144 81.91.80.145 81.91.80.146 81.91.80.147 81.91.80.148 81.91.80.149 81.91.80.150 81.91.80.151 81.91.80.152 81.91.80.153 81.91.80.154 81.91.80.155 81.91.80.156 81.91.80.157 81.91.80.158 81.91.80.159 81.91.80.160 81.91.80.161 81.91.80.162 81.91.80.163 81.91.80.164 81.91.80.165 81.91.80.166 81.91.80.167 81.91.80.168 81.91.80.169 81.91.80.170 81.91.80.171 81.91.80.172 81.91.80.173 81.91.80.174 81.91.80.175 81.91.80.176 81.91.80.177 81.91.80.178 81.91.80.179 81.91.80.180 81.91.80.181 81.91.80.182 81.91.80.183 81.91.80.184 81.91.80.185 81.91.80.186 81.91.80.187 81.91.80.188 81.91.80.189 81.91.80.190 81.91.80.191 81.91.80.192 81.91.80.193 81.91.80.194 81.91.80.195 81.91.80.196 81.91.80.197 81.91.80.198 81.91.80.199 81.91.80.200 81.91.80.201 81.91.80.202 81.91.80.203 81.91.80.204 81.91.80.205 81.91.80.206 81.91.80.207 81.91.80.208 81.91.80.209 81.91.80.210 81.91.80.211 81.91.80.212 81.91.80.213 81.91.80.214 81.91.80.215 81.91.80.216 81.91.80.217 81.91.80.218 81.91.80.219 81.91.80.220 81.91.80.221 81.91.80.222 81.91.80.223 81.91.80.224 81.91.80.225 81.91.80.226 81.91.80.227 81.91.80.228 81.91.80.229 81.91.80.230 81.91.80.231 81.91.80.232 81.91.80.233 81.91.80.234 81.91.80.235 81.91.80.236 81.91.80.237 81.91.80.238 81.91.80.239 81.91.80.240 81.91.80.241 81.91.80.242 81.91.80.243 81.91.80.244 81.91.80.245 81.91.80.246 81.91.80.247 81.91.80.248 81.91.80.249 81.91.80.250 81.91.80.251 81.91.80.252 81.91.80.253 81.91.80.254 81.91.80.255 + 1.8K more (range too large to list inline)

BGP Routing

Live BGP anomalies →

This block is announced in BGP, observed across our RIPE RIS collectors.

Announced prefix
81.91.80.0/21
Origin AS
AS39790
Announcement samples
27,577
Last seen
2026-10-15 11:57:04

Frequently Asked Questions

What is 81.91.80.0/21?

81.91.80.0/21 is a CIDR network block containing 2,048 IPv4 addresses (from 81.91.80.0 to 81.91.87.255). CIDR notation combines an IP address with a prefix length to define a range of addresses.

Who owns the 81.91.80.0/21 network?

The 81.91.80.0/21 range is allocated to Web4U s.r.o. and announced via AS39790 from Czechia.

Last updated: 2026-10-15 12:24:05 UTC
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