It's much easier for most people to reference charts of netmask/genmask/CIDR values vs. trying to remember them (though some common masks such as 0 and 255 are easy enough).
Below the chart are a few links to various related tools.
Static Chart
CIDR Conversion Table | ||||||
---|---|---|---|---|---|---|
CIDR Prefix Length | Dotted Decimal Netmask | Hexidecimal Netmask | Inverse Netmask (Wildmask) |
Binary | Number of Classful Networks | Number of Usable IPs |
/1 | 128.0.0.0 | 80 00 00 00 | 127.255.255.255 | 1000 0000 0000 0000 0000 0000 0000 0000 | 128 A Class | 2,147,483,646 |
/2 | 192.0.0.0 | C0 00 00 00 | 63.255.255.255 | 1100 0000 0000 0000 0000 0000 0000 0000 | 64 As | 1,073,741,822 |
/3 | 224.0.0.0 | E0 00 00 00 | 31.255.255.255 | 1110 0000 0000 0000 0000 0000 0000 0000 | 32 As | 536,870,910 |
/4 | 240.0.0.0 | F0 00 00 00 | 15.255.255.255 | 1111 0000 0000 0000 0000 0000 0000 0000 | 16 As | 268,435,454 |
/5 | 248.0.0.0 | F8 00 00 00 | 7.255.255.255 | 1111 1000 0000 0000 0000 0000 0000 0000 | 8 As | 134,217,726 |
/6 | 252.0.0.0 | FC 00 00 00 | 3.255.255.255 | 1111 1100 0000 0000 0000 0000 0000 0000 | 4 As | 67,108,862 |
/7 | 254.0.0.0 | FE 00 00 00 | 1.255.255.255 | 1111 1110 0000 0000 0000 0000 0000 0000 | 2 As | 33,554,430 |
/8 | 255.0.0.0 | FF 00 00 00 | 0.255.255.255 | 1111 1111 0000 0000 0000 0000 0000 0000 | 1 A or 256 Bs | 16,777,214 |
/9 | 255.128.0.0 | FF 80 00 00 | 0.127.255.255 | 1111 1111 1000 0000 0000 0000 0000 0000 | 128 B Class | 8,388,606 |
/10 | 255.192.0.0 | FF C0 00 00 | 0.63.255.255 | 1111 1111 1100 0000 0000 0000 0000 0000 | 64 Bs | 4,194,302 |
/11 | 255.224.0.0 | FF E0 00 00 | 0.31.255.255 | 1111 1111 1110 0000 0000 0000 0000 0000 | 32 Bs | 2,097,150 |
/12 | 255.240.0.0 | FF F0 00 00 | 0.15.255.255 | 1111 1111 1111 0000 0000 0000 0000 0000 | 16 Bs | 1,048,574 |
/13 | 255.248.0.0 | FF F8 00 00 | 0.7.255.255 | 1111 1111 1111 1000 0000 0000 0000 0000 | 8 Bs | 524,286 |
/14 | 255.252.0.0 | FF FC 00 00 | 0.3.255.255 | 1111 1111 1111 1100 0000 0000 0000 0000 | 4 Bs | 262,142 |
/15 | 255.254.0.0 | FF FE 00 00 | 0.1.255.255 | 1111 1111 1111 1110 0000 0000 0000 0000 | 2 Bs | 131,070 |
/16 | 255.255.0.0 | FF FF 00 00 | 0.0.255.255 | 1111 1111 1111 1111 0000 0000 0000 0000 | 1 B or 256 Cs | 65,534 |
/17 | 255.255.128.0 | FF FF 80 00 | 0.0.127.255 | 1111 1111 1111 1111 1000 0000 0000 0000 | 128 C Class | 32,766 |
/18 | 255.255.192.0 | FF FF C0 00 | 0.0.63.255 | 1111 1111 1111 1111 1100 0000 0000 0000 | 64 Cs | 16,382 |
/19 | 255.255.224.0 | FF FF E0 00 | 0.0.31.255 | 1111 1111 1111 1111 1110 0000 0000 0000 | 32 Cs | 8,190 |
/20 | 255.255.240.0 | FF FF F0 00 | 0.0.15.255 | 1111 1111 1111 1111 1111 0000 0000 0000 | 16 Cs | 4,094 |
/21 | 255.255.248.0 | FF FF F8 00 | 0.0.7.255 | 1111 1111 1111 1111 1111 1000 0000 0000 | 8 Cs | 2,046 |
/22 | 255.255.252.0 | FF FF FC 00 | 0.0.3.255 | 1111 1111 1111 1111 1111 1100 0000 0000 | 4 Cs | 1,022 |
/23 | 255.255.254.0 | FF FF FE 00 | 0.0.1.255 | 1111 1111 1111 1111 1111 1110 0000 0000 | 2 Cs | 510 |
/24 | 255.255.255.0 | FF FF FF 00 | 0.0.0.255 | 1111 1111 1111 1111 1111 1111 0000 0000 | 1 C | 254 |
/25 | 255.255.255.128 | FF FF FF 80 | 0.0.0.127 | 1111 1111 1111 1111 1111 1111 1000 0000 | 1/2 C Class | 126 |
/26 | 255.255.255.192 | FF FF FF C0 | 0.0.0.63 | 1111 1111 1111 1111 1111 1111 1100 0000 | 1/4 C | 62 |
/27 | 255.255.255.224 | FF FF FF E0 | 0.0.0.31 | 1111 1111 1111 1111 1111 1111 1110 0000 | 1/8 C | 30 |
/28 | 255.255.255.240 | FF FF FF F0 | 0.0.0.15 | 1111 1111 1111 1111 1111 1111 1111 0000 | 1/16 C | 14 |
/29 | 255.255.255.248 | FF FF FF F8 | 0.0.0.7 | 1111 1111 1111 1111 1111 1111 1111 1000 | 1/32 C | 6 |
/30 | 255.255.255.252 | FF FF FF FC | 0.0.0.3 | 1111 1111 1111 1111 1111 1111 1111 1100 | 1/64 C | 2 |
/31 | 255.255.255.254 | FF FF FF FE | 0.0.0.1 | 1111 1111 1111 1111 1111 1111 1111 1110 | 1/128 C | 0 |
/32 | 255.255.255.255 | FF FF FF FF | 0.0.0.0 | 1111 1111 1111 1111 1111 1111 1111 1111 | 1/256 C | 1 |
Links to Interactive Tools
- A chart with Cisco masks
- Interactive CIDR calculator
- IPv4 and IPv6 tools for decimal conversion, CIDR, ping, and traceroute