CIDR reference table, private ranges, reserved blocks and subnet sizes.
| CIDR | Netmask | Addresses | Usable hosts |
|---|---|---|---|
| /32 | 255.255.255.255 | 1 | 1 |
| /31 | 255.255.255.254 | 2 | 2 |
| /30 | 255.255.255.252 | 4 | 2 |
| /29 | 255.255.255.248 | 8 | 6 |
| /28 | 255.255.255.240 | 16 | 14 |
| /27 | 255.255.255.224 | 32 | 30 |
| /26 | 255.255.255.192 | 64 | 62 |
| /25 | 255.255.255.128 | 128 | 126 |
| /24 | 255.255.255.0 | 256 | 254 |
| /23 | 255.255.254.0 | 512 | 510 |
| /22 | 255.255.252.0 | 1,024 | 1,022 |
| /21 | 255.255.248.0 | 2,048 | 2,046 |
| /20 | 255.255.240.0 | 4,096 | 4,094 |
| /19 | 255.255.224.0 | 8,192 | 8,190 |
| /18 | 255.255.192.0 | 16,384 | 16,382 |
| /17 | 255.255.128.0 | 32,768 | 32,766 |
| /16 | 255.255.0.0 | 65,536 | 65,534 |
| /15 | 255.254.0.0 | 131,072 | 131,070 |
| /14 | 255.252.0.0 | 262,144 | 262,142 |
| /13 | 255.248.0.0 | 524,288 | 524,286 |
| /12 | 255.240.0.0 | 1,048,576 | 1,048,574 |
| /11 | 255.224.0.0 | 2,097,152 | 2,097,150 |
| /10 | 255.192.0.0 | 4,194,304 | 4,194,302 |
| /9 | 255.128.0.0 | 8,388,608 | 8,388,606 |
| /8 | 255.0.0.0 | 16,777,216 | 16,777,214 |
| Range | CIDR | Use |
|---|---|---|
| 10.0.0.0 – 10.255.255.255 | 10.0.0.0/8 | Private (RFC 1918) |
| 172.16.0.0 – 172.31.255.255 | 172.16.0.0/12 | Private (RFC 1918) |
| 192.168.0.0 – 192.168.255.255 | 192.168.0.0/16 | Private (RFC 1918) |
| 100.64.0.0 – 100.127.255.255 | 100.64.0.0/10 | Carrier-grade NAT (RFC 6598) |
| 127.0.0.0 – 127.255.255.255 | 127.0.0.0/8 | Loopback |
| 169.254.0.0 – 169.254.255.255 | 169.254.0.0/16 | Link-local / APIPA |
| 192.0.2.0 – 192.0.2.255 | 192.0.2.0/24 | Documentation (TEST-NET-1) |
| 198.18.0.0 – 198.19.255.255 | 198.18.0.0/15 | Benchmark testing |
| 224.0.0.0 – 239.255.255.255 | 224.0.0.0/4 | Multicast |
| 240.0.0.0 – 255.255.255.254 | 240.0.0.0/4 | Reserved |
| 255.255.255.255 | 255.255.255.255/32 | Broadcast |
| Port | Service |
|---|---|
| 20 / 21 | FTP |
| 22 | SSH / SFTP |
| 25 | SMTP |
| 53 | DNS |
| 80 | HTTP |
| 110 | POP3 |
| 143 | IMAP |
| 443 | HTTPS |
| 465 | SMTPS |
| 587 | SMTP submission |
| 993 | IMAPS |
| 995 | POP3S |
| 3306 | MySQL / MariaDB |
| 3389 | RDP |
| 5060 / 5061 | SIP (VoIP) |
| 5432 | PostgreSQL |
| 8006 | Proxmox |
| 10000–20000 | RTP (VoIP media) |
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