Routes and Rules

Netmask/Genmask Conversion Table

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